I've been DMing for a few years. Mostly I've done pre-made WoC content. We're about to finish Strahd. I am planning to run my first pseudo-homebrew. Going to work in an established setting but the plot will be mine. I'm struggling with how to move from the little individual adventures into major plot elements. Any thoughts? 

For starters, what are your major plot elements? From those you can sort of build something of a campaign skeleton with the major beats framing the smaller adventures.

In your spare time, think back on those mini-adventures and try to figure out what the NPCs or monsters or even environmental hazards were doing there.  Then, work on tying stuff together. 

A few questions. Do you have a campaign theme? How many players at what level? What setting are you hoping to use? Which of the pillars are you planning on focusing on? Combat, Exploration, or Social?

Work with your players. Ask them what they want to do. An easy way to broach it is asking who and what they want to fight. A campaign of hunting drow and mind flayers in the Underdark is gonna be much different then fighting lizardfolk and dragons in the jungle. The things they want to fight are gonna determine a lot of where the adventures take place and what story elements you'll be using.

Furthermore, get your players to really invest in making a backstory. That'll give you some ideas where the adventure could head in time. Have your bard find a clue leading to the relic he's dedicated his studies to finding, and have it be something useful for defeating the Giants whose invasion is your current campaign arc. Have the orc tribe that destroyed your ranger's village as a child pledge allegance to the necromancer trying to destroy the kingdom. They'll tell you everything about the kind of adventures they want to have through their character's backstory.

Just those two tactics will give you a lot of direction and take a ton of weight off your shoulders. If you're still having trouble from there, steal stuff. Look up one shots and modules online and reap the ideas they have. Take a door puzzle from this one, a good NPC from that, creative setups for encounters from yet another. It doesn't take much polish to make a stolen idea look original, and even if it's not it'll still be fun. If WotC will describe the rolling boulder trap from Indiana Jones as a viable option right in the DMG, then you can sneak away with copying a room or puzzle from some other game. Always give credit, but steal without remorse.

Thanks for the replies guys and gals. To answer the questions asked...

The group is 4-5 players, starting at level 5 and planning for level 20. They want to at least end up doing real hero stuff. Saving the realm, fighting big baddie monsters like dragons, beholders, foiling big plots. 

We're going to adventure in Matt Mercer's Tal'dorei but the campaign and plot are my own. I wanted a place with framework that I knew but my players don't. 

Again thanks so much for the help

Okay, I don't know a thing about your setting, but here's something:

The PCs are hired to clear out a haunted crypt ruled by a buffed-up bone naga.  After defeating the naga in its lair, they are forced to flee an alhoon. 

Throw in something with a telepathic fomorian and its mindwitness minion; something with rather a lot of chuul, giant crayfish, hulking crabs, and maybe even giant crabs (you could even throw in a young blue dragon if you wanted to); something with a colony of gricks and a grick alpha; something with githyanki and their mindwitness minion; and something with a death kiss and its pet mindwitness in here somewhere. 

Remember that crypt?  And the alhoon?  It's rematch time!  After defeating the alhoon (and its pet mindwitness) in its all-too-familiar lair, the PCs are forced to flee a death tyrant. 

By around 9th or 10th level, they've managed to find enough clues to find the mind flayer colony they're supposed to go after--and become convinced that said mind flayers are the campaign's main villains.  The colony has a mindwitness and an elder brain.  Unless the PCs destroy the pool with the tadpoles in it, they'll have to deal with a neothelid at some point in the future. 

The PCs should now be around 11th or 12th level.  It's time to deploy the fiends; yugoloth mercenaries (and their pet mindwitness) hired to destroy everything the PCs are known to hold dear; a devourer and its army of undead; a secret cult of suicidally idiotic nobles trying to invite a nalfeshnee to tea at the instigation of what appears to be a mindwitness; a bheur hag and its abominable yeti and ice devil minions, not to mention the nearby frost giants and ice trolls--and the frost giant everlasting one that is an obvious consequence thereof (this is a good opportunity to use an adult white dragon, or possibly even an ancient white dragon); and a (possibly modified) war priest that tried to summon an angel but got an erinyes instead. 

Now they get to go deal with that death tyrant and its pet mindwitness.  Turns out it was the only thing keeping the crypt from caving in.  Oops. 

How about a herd of hellephants and a few party-level-appropriate devils, accompanied by yet another mindwitness? 

Next, the PCs get to go to an active volcano to break up a cult of Imix.  Later, an ancient red dragon decides to take over the lair--or so the PCs think; it was there the whole time.  Just after the PCs kill it, a beholder that can cast misty step at will and as a legendary action shows up and starts trying to make the volcano erupt, having long since relieved the dragon of its treasure.  The beholder flees if it looks like it might lose. 

The PCs should spend the next few sessions, if not the next few levels, hunting down that beholder, only to discover (by killing it) that it's merely a very lifelike illusion created by an aboleth, the real main villain.  Don't make it easy to find the aboleth, either. 

When the PCs kill the aboleth, it laughs, telepathically informs them that the entire adventure has gone all according to its plan, and dematerializes.  Cue a trip to the PCs' favorite really good library (they should have one by now), followed by a trip to the Elemental Plane of Water. 

Since you're playing in the Tal'dorei campaign setting, maybe have your players be members of the Slayer's Take hunting guild in Vasselheim. This would provide you with some great adventure hooks early on in the campaign to level up your PC's and could potentially lead to larger adventures by tying in pre-existing characters like Zahra and Kashaw. 

There is a campaign idea I found in game from FASA - the adventure was called Harlequin - and its not DND, but its stuck with me.

The plot (story) is important, but what the module impressed upon me was that pacing was critical.  Once you get the outline and the major character's BBEG, BGNC (Big Good Nice Guys) and their motivations and machinations all worked out... 

remember to space it out.  1 Session "on point" - directly involved with the underlying plot line.  1-2 sessions spent on something else, then move to 1 session on, 1 session off, then 2 sessions on 1 session off, then FULL BORE move to resolution/climax.

It really brings players a sense of urgency and pacing, and allows some breathing room to adjust, relax and refocus.

First decide antagonist type, the way I see things is below:

1)Bestial- Basically a creature or group of creatures the players need to stop. They react based on magical abilities and instinct. This type of any is best for a one shot or a small multi-session type game. I'd avoid doing this as your campaign base.

2)Environmental- This is where the players are given a challenge that can't strictly just kill. This could be a magical curse disease, entropy, or even an extremely strong monster. For example, an ancient red dragon probably won't be combat killed directly by your level 1 party any time soon so they might be on a quest for an adventurer that can. These work best when the party is seeking out an object or group of objects that can accomplish there objectives. Simply decide number of objects and how many challenges they must overcome to get them. Any challenge that doesn't give them a item gives them a clue to the next location. So come up with a couple cool challenges and make a little diagram. Then add some traveling challenges, mystery, and interconnections between challenges. You are pretty much done with the plot at that point. Its really just refinement.

3)Organizational- The party is fighting a faction or groups of factions each trying to achieve a nefarious goal. This is my favorite as it is the most open ended. List each faction and its goals. Then add npcs to each faction and add personal goals and factional goals to each npc. Consider a few ways the players might actually stop these factions and keep them in your back pocket... Really your writing stops here after some refinement. After each session consider party actions and how it affects npc and faction goals. Then adjust their behavior accordingly.