I'm looking for a bit of help. My campaign is going pretty good at the moment, my players are at level 7 and we've been playing for over a year now. However, I've realised that all we've been doing for a long time is focusing on the main quests, and I can feel my players are eager to switch things up a bit with some side adventures. But I absolutely suck at designing those, it seems I can create main plots. So, I'm looking for ideas or advice on how to create some.

If you're keen to give ideas, here's a little bit about the world:

Currently, the world is pretty post-apoc, the material plane having combined with the shadowfell. There are two safe places, the city where the players come from, and a Dwarven city in the mountains. Cities are overpopulating and suffering from unrest. Shadows and demons and cultists live in the wilds. Most of the gods locations are unknown.

The players are part of a "heroes guild" who are the only ones allowed to explore the wilds, working to clear it of dangers. They also work for the ruler of the city. There are some other organisations around including an underground Bloodhunter's group and something similar to the Red Jennys from Dragon Age. 

Any ideas/advice seriously welcomed.

I've had players kidnapped at night while asleep, town/village folk starting to catch an 'outbreak' of a disease/etc, local water/food sources being poisoned, mysterious graffiti marks around town (on certain doors, etc), and so on.  As a side quest, form a cause for concern, but not a directly actionable item.  These quests will take active investigation and logic to sort out the cause and potential reasoning behind it.

Night Hags are particularly fun when they're the mysterious newcomer who manage to seduce an important town official or key person of interest.

Well, you know what they say, no campaign is complete without a detective. Side quests can be difficult to come up with at times, I agree that main plots are much easier, but there is a pretty interesting solution. Add a private detective (Or something of the sort) that sends the player on a quest for clues, or something along the lines. In my own campaign, I have a Goblin Detective who can cast basic cantrips (So, he's a bit like Constantine). My players are attempting to find out information, and are pointed toward him for guidance, seeing as he is a detective and all. Turns out, he knows nothing about the person my PCs are looking for, but, he has an offer. 

"Wait!" the goblin says frantically, "I may not have your information, but I have a proposition to make!"

The detective goblin wants help to track down a demon that has committed a string of killings. Something along these lines is nice to mix up epic quests. Instead of intense fight scenes, the players are hunting for clues and tracking down the demon before they get the sweet finish of killing it. Usually, a side quest has some sort of small reward that can help the players with the big bad. And, it's a good idea to involve the PCs personally in the quest. For instance, the demon my PCs are hunting turns out to be the demon that killed our Rogue's parents. 

I hope this helps you a bit (And remember to put your own spin on it) 

Good luck, Paradox52

Recently my DM created side quests for us to do to get us between his main quest locations.  Unfortunately for him, we decided the main quest was too big to complete with anything short of an army and offered no promise of payment while the side quests were far more interesting, achievable, and rewarding.

I use 2 strategies. 1. Encounters during travel that delay the party but don't fully bump them off course, and 2. Player backstories. I'll give an example of each from my game.

1. Encounters on the road that temporarily sidetrack the party

The main story in my game is currently a mysterious plague of undeath.  My players are investigating the source of the undead that have been coming forth from the mountains and terrorizing small villages along the foothills. Their travel took them through a small trading town where, while staying the night, they caught the attention of the local guild leaders who needed help with a bandit problem. They had a standing agreement to pay a small sum to the bandits to leave their shipments alone, but a recent change in bandit leadership has seen the thieves violate that agreement. The guild leaders offered the party money to a) retrieve their most recent stolen shipment, b) purge the bandits from their hideout for good, and they offered a potential "something extra" to c) return with credible information on who the bandits were now working for that caused them to violate the agreement. This simple side quest took three sessions and didn't knock them off course because they returned with the package and went on their way. You can drop little missions like that all over the place while your players are travelling. Maybe they bite, maybe they don't, but all you can do is throw out some hooks and hope they go for it.

2. Backstory

In the above bandit quest, the players found a shipping ledger detailing where the bandits had been sending their pilfered goods. One of the addresses in the ledger was the family shop of the Ranger of my party. The only problem, his tragic backstory involved the shop shutting down after his brother, the former owner of the shop, was murdered about 5 years back (no body was found). The player hasn't been back to his home city, so this came as a huge shock to him, and now the party is pulled in 2 directions as they want to go to this city as soon as they realistically can. 

So here's an example that peppers in a little bit of both 1&2 for your setting

Maybe a few people from one of your character's past belong to one of the underground organizations that exist in your world. The party is out on a main investigatory mission and they run into faction members of this organization, and after a brief confrontation they realize that someone that your character knows from the past is in this group and they recognize one another. This NPC needs help with whatever they were doing at the time, perhaps rescuing another old friend who was sent out to scout some location looking for *insert fabled ancient artifact that was said to have been lost in the shadowfell* and they haven't returned. Hopefully the party is compelled to help due to personal connections, and you have a 3-5 session arc that delays the party on the main quest but doesn't make them abandon it altogether. Perhaps this leads to increased connections within this underground organization as well, which could open up side quests relating to those down the line

Lately, when I have been designing an area that the main story will take players into, I try to come up with about a dozen single paragraph throwaway story hooks. That way I have some filler if I need to adjust the pacing of the session and if something interesting happens, it can be expanded into a more meaningful story or I can tie it into a larger story in some way. I have also discovered that the less specific I am when making these story hooks, the more likely I will be able to recycle unused hooks into a future area. Before long, you will have several dozen drop-in story hooks for side quests and out of those, maybe a dozen or more are likely going to be appropriate for the area your players are in.

Example:

1. On a large island is an ancient ruined lighthouse from a civilization long forgotten. The stones of the tower seem to have been hewn from one particularly robust stalagmite with a spiral staircase winding around the outside, ascending twenty feet to a flat platform on the top. A stone beacon atop the tower has not been lit in ages. There are instructions chiseled into the stone wall near the beacon in dwarvish describing instructions for maintaining the lit beacon and the importance of keeping good visibility for safe water traffic. If PCs light the beacon, it emits light that can be seen across the lake for several miles. If the beacon is lit, it also calls forth the banshee of a drow captain named J’zarra and five lacedons who were her crew before their ship ran aground long ago on the island when the beacon had not been lit to guide their way safely. They despise anyone who attempts to light the beacon and will not stop attacking unless they are destroyed or until the light is snuffed out. If searched, the waters just off the island (DC15) reveal the preserved remains of an old ship with a chest below deck that containing a small treasure of money and gems worth 150gp, and a sealed potion of greater healing.

It's a disposable encounter, but it has enough flavor to be interesting. If the players latch on to the old lighthouse or the old ship, then I can make a backstory about one or both of them and work it into the game in the future.

I have an idea for my campaign as a side thing is a reoccurring NPC that is an inventor (known for making the first firearms, then tries to outdo himself) that makes the first clockwork man (which malfunctions), then a clockwork hound (which malfunctions), then eventually hired to create a clockwork dragon (see a theme yet?) Soon he will invent the first airship. These should give all kinds of side quest ideas. Hope it helps!

For campaigns I run I always make sure to create a variety of side quests/throwaway chance encounters to add to the randomness.  I will almost always have a couple traveling merchant types that will try to sell minor cursed items that aren’t what they seem, but who’s detriments are not normally enough to be outright bad (just annoying/a hindrance).  Sometimes I will add in the trope-ic amnesia afflicted Paladin NPC who is being tormented by an evil deity trying to slowly corrupt them into a Warlock style pact for some semblance of power they once had access to as a Paladin (usually as they mistakenly believe they are being kidnapped by ‘bandits/etc’ from helpful NPC travelers.  A lot of my minor encounters are also pun based, so that gives me extra entertains value as the PC’s try to uncover the clever word play (some more obvious than others).  My favorite mini/side quests are the seemingly non attached fetch quest style ones (like in many Legend of Zelda games) where the party has to collect seemingly random items for any number of stranger NPC’s that all eventually lead to whatever special artifact/items you want them to end up with. 

I also like to play with player expectations with missions, sometimes having quests that split the party, (having one or two members being hired to find and deliver/rescue a certain NPC.  While the other PC’s are hired by another different NPC to escort/protect an NPC.  Only for the PC’s to all discover the first NPC had hired his group of PC’s to find/deliver the last remains exiled heir of a kingdom/providence and the other PC’s were hired to protect the heir from said usurper.  Or have the PC’s have a go at match-making between a number of potential marriage arrangements needed to build future alliances among potential rival factions.  Only each NPC involved has a secret agenda that may or may not go against their publicly stated choice/agenda (Like a certain queen who secretly worships a demon/devil) saying she wants her son to marry a Half Orc chief’s daughter for political stability but really just wants to be able to sacrifice ‘monstrous spawn’ AKA her grandchildren to her deity.  The prince meanwhile can state he would take the Elven princess’s hand to wed because of her beauty, but he would rather marry someone else because they share certain hobbies/past times/ has a preferred gender attraction that is not normally accepted in that society, and so on and so forth.  This gives the PC’s several layers of investigation as they uncover each party’s secret agenda/desire(s) and try to balance the surface demands.  As well as consider the overall lasting effects and consequences of their actions on the Good of the Many vs rights of the few spectrum, and the discipline vs freedom axis.  Then there’s the whole introduction to various factions concept to add a whole new level of side quest goodness to.

Use your players for side quests. Im sure they have their own ideas as to what is going on in the game world. Take hold of that info and build on it. It really messes with the players. I design my quests as simple notes without to much detail this way its not a total wast if they pass it up. With that said you can use it later in one way or another because they never acted on it. They might not be able to purchase needed goods from a NPC vendor because they did not help them. Or all the towns folk are ill because the group did not find a source of the illness. Anyway you can go crazy with stuff. Keep you game sessions updated and make changes to quests before or after every session. This will help keep things fresh.