How do I split up my party without causing issues?

My players have split into two different investigation parties in our most recent session, but the issue is that I don't know how to make it engaging for them. I wasn't really expecting this, and tried to roll with it, but I'm scared I'll either spend too much time on one party, as 'Party 2', is investigating stuff that's far more important/story-relevant, but I don't want to make Party 1 feel bored. Any suggestions from anyone familiar with this??

I did this when I was running the Stygian Gambit adventure. What helps is if you have a map, then you can figure out where everyone is. Also, a good strategy is to cut back and forth at climatic moments, so that you keep everyone excited.

My party was caught and thrown into prison, each to their own cell scattered around the dungeon. What I did was I had them throw initiative to see which order they would act. But I didn't have them make only one action per turn. Instead, their turn lasted for a minute or two until it was the next player's turn. That way they could spend for example ~20 seconds trying to listen to approaching guards or other voices before they attempted to pick/break the lock, and they would still have time to get a look what is behind the door before their turn was over. Eventually the party members found each other and became a split party of two each. Once two party members found each other, they shared initiative from that moment onward and they shared a turn.

thanks for the advice, I'll try this out. 

Quote from BruenorBattlehammer1277 >>

My players have split into two different investigation parties in our most recent session, but the issue is that I don't know how to make it engaging for them. I wasn't really expecting this, and tried to roll with it, but I'm scared I'll either spend too much time on one party, as 'Party 2', is investigating stuff that's far more important/story-relevant, but I don't want to make Party 1 feel bored. Any suggestions from anyone familiar with this??

 
Yeah my Monday night group laugh in the face of 'don't split the party'. The way I try to handle things is to shift the spotlight equally. So, spent ten minutes at a time (or however long feels engaging just split the time equally) before shifting the spotlight and finding out what the other party are up to. 

In one session I literally had two player characters head into a Beholder's Lair while two other player characters spent the same time sitting in the garden of a tavern watching the butterfly that kept flitting between flowers, and just enjoying the peace and quiet. The players all seemed to enjoy the events of both parties they all got to do the things that they wanted to do and it made for some absolutely wonderful moments. 

The other tack you could take is spread out the clues. If you've intended to find a satchel monogrammed with a suspect's initials and a signed letter to be found in a location - split those items up so they're each found in a separate location. In my view this doesn't tend to work as well, but it can work. 

Try to engage everyone and be a little more lenient than you'd normally be. Let group one pull off some shenanigans that you might not normally, let them have plenty of laughs while group two digs up important info that makes them feel like they're doing a good job.

Well, there's a reason "don't split the party" is a maxim. In general your solutions are

1. Alter the story to make the 'less important/story relevant' path more important or interesting -- maybe certain pieces of information are available from multiple sources (though this gets into quantum ogre territory), maybe you just add something to the story.
2. Make it clear quickly that this is a dead end, and let them go do something else.
3. Introduce something entertaining but not plot relevant (as long as the players are having fun, forwarding the plot is entirely optional).

I agree with @LinkArcher. It has worked well for me. 

I am wondering how your question morphed from What Issues can I cause my Party When they Split Up? :). I don't set out to kill ANY PC, but if you split up, I'll nudge more.

Quote from JohnnyC1971 >>

I agree with @LinkArcher. It has worked well for me. 

I am wondering how your question morphed from What Issues can I cause my Party When they Split Up? :). I don't set out to kill ANY PC, but if you split up, I'll nudge more.

 The more you split unnecessarily, the more likely you are to “accidentally “ run into party difficulty adventures…

As a player I hate splitting the party unless someone is trying to do a stealth mission or something. My players did a couple that turned out very well, but it fit the story and ended up being a lot of fun... but I was prepared for them.

 I some how did this well with my party during a trial. 

The set up is, my party came into this old west inspired town, caught the wanted bad guy and one of them was named Sherif. The bad guy goes on triral, during which the party finds out his gang has kidnapped the Judges grand daughter. If the trial is stopped, or the bad guy is found guilty the granddaughter is killed. 

So the party spilt, 3 stayed at the courthouse, the bard  (playing the part of the prosecution), the fighter (the sheriff), and the sorcerer because she was a witness. The other 5 players (I have a big party, it's a store-sponsored game) went to the old mining camp to rescue the girl. The actual combat was kinda tedious, because they were level 6 going against bandits, but I contrasted that with flipping back to the courtroom every few rounds so the bard could be entertaining, as they stalled for time basically, it actually made for a interesting session or two where both groups got to kinda stand out. 

I just had my party split and investigate two different clues last session.

What works is to try to get each group to work in "chunks" of time, and then toggle back and forth each chunk.

PlayerGroupARogue: we want to follow the one-armed man and see where he goes.

DM: he is taking some back alleys and such. I will need a Survival Check to track him, and stealth checks to see if you remain hidden.

GroupARanger: i cast Hunters Mark! Now we can hang back a bit more and not have to be right on too of him.

Dm: give me a survival chec at advantage.

Ranger: 27! 

Dm: ok. You are able to track his every move. Everyone give me a stealth check. DC 15.

PartyA: 23! 18. 28!

Dm. Ok. Youll follow him through the streets for a while. It will take a while before he gets to his destination, wherever that is. Lets go to the other group. What are you doing?

PartyB: artificer: check this location for clues!

Bcleric: cast speak with dead!

Dm:to artificer: give me an investigation check.

Artificer: 27

Dm: it will take several minutes to search, but you will find (reads notes from campaign book)  cleric: the corpse moves and sits up, looking at you.  

Cleric: we are here to catch the man who murdered you. What happened here?

DM: (gives a quick sequence of events for the last few minutes leading up to the murder)

Cleric:(asks 2 more questions)

Dm: (gives answers) the corspe slumps to the ground.  Ok. Lets switch to GroupA: you follow the one armed man through the city until he goes into the Rag and Bone tavern, via a door in the alley.

GroupARogue: to ranger: make sure he doesnt sneak out the back. Ill go in the front and talk to the bartender.  He's helped me before.

And so on.

A "chunk" is basically whatever the players can do in maybe 5 minutes of real world time before the other group gets bored. If youre revealing information that is interesting to everyone, then the other charavters might be somewhere else and wont know until later, but the players are at your table listening intently. So you can go a little longer.

Whenever you feel like you hit a point of "ok thats done" switch to the other group.

When everyone is together time doesnt matter so DMs and players iften forget this, but things like doing a perception check on an entire room takes like ten minutes in game. That how long it takes to comb through everything and find the chest hidden in the closet. 

The player who finds the chest will immediately want to pick the lock, but to keep everyone engaged, you will need to enforce the passage of time. Tell the artificer what they find when they investigate the room. When they want to pick the lock, tell them it took ten minutes to search te room, so you will switch to the other players. This gives them something to think about while they are waiting. If they find some papers with clues on it, hand the paper to them now, and go to the next player. While the artificer is waiting they will be reading and rereading the paper trying to decipher the clues.

There used to be a thing called "dungeon turns".  It was basically how we handled dungeon crawling when there wasnt combat. Basically everyone got ten minutes to do a thing. Search a room for secrets took ten minutes. Read and decypher runes on a wall, took at least ten minutes. 

It basically allowed thr dm to go around the table and ask "what are you doing?" And each person could get one thing done.

You want the same "chunky" approach to time for your split party, let each player in the split groups do a thing, and that thing should take a "chunk" of time.