I recently picked up Out of the Abyss and was wondering what tips or tricks I should keep in mind when I get around to running it. 

After running my last module (Curse of Strahd), there were a handful of things I realized I should have put more emphasis on to make the adventure more enjoyable as well as a handful of things I should have been more cautious about allowing the party to do so as to keep the encounters balanced. 

I have just begun reading over the module and one question sticks out to me as an example of the type of guidance I am looking for: When the party is creating characters, should I let them know up front that their PCs are going to be imprisoned at the start of the adventure or leave that as a surprise? 

Tell your players up front. Explain it is an underdark adventure. I have run this twice now and was going to try and be a bit clever the first time and manipulate things so the party got captured but after reading a couple of bits of advice online I decided to tell them and think it was much better for it. Over all the campaign is really good but does need a lot more up front prep then most, and I include CoS in that. I didn't tell them the name of the campaign (I covered the book) because I didn't want any hint this was a demon based adventure. 

I used this guide 
https://www.elventower.com/out-of-the-abyss-guide/

Be aware that if there are non dark vision characters then very quickly things can get a bit irritating. In both campaigns I have run there was a human character. I let them struggle for a while, (you can do things like have bio luminescent fungi in areas etc so it isn't pitch black all the time) but I allowed them to find some goggles of dark vision by about level 3/4. It is another good reason for explaining the basis of the adventure (being captured and in the dark), some players will love playing a blind character session after session loving the challenge, others will hate it and really dislike the game so give them a chance to understand the situation. 

In the first run through my party escaped with none of there equipment, that was a decision they made, the second run through the party took a lot longer planning the escape and managed to find everything. In the first instance I had to get very creative with allowing characters to make daggers from flint, turn bits of stick into a focus etc. Alot of that I needed to do on the fly because I had not prepared for them not to get anything. 

The dwarven city Gracklstugh needs a lot of work, it is one of the weakest areas in the book, there are some plot threads in the book that are just left unfinished, or have barely a sentence that describes potentially sessions of game play. I ended up buying a homebrew module to help me fix this chapter for the first run and I then tweaked things again for the second. 

The NPC's, you have 10 important NPC's that you need to bring to life, manage, control and use as makes sense to help the party. many of them will remain with the party for the initial chapters in the book, as a DM that can get draining, so be prepared for that. 

The Demagorgon :- The first time the characters meet the Demagorgan they will have to run, it is a guaranteed TPK moment otherwise. The first time I ran through it I really could have made it more impactful in terms of how I described it and painted that picture. A real escape through the town as the demagorgon destroyed it and slaughtered everyone. The second time I learnt from this and was inspired by some of the "escape" levels in mid 2000's computer games, providing a series of scenes and skill checks to add tension, never with the intention of it killing the party but the players didn't know that. Also be aware, depending on how this plays out the party might lose a lot of there stuff again in the escape. remember they are prisoners again, in my case they did, and so I allowed them to sneak back into the ruins of the town after to find and collect them rather then start all over again. 

If I think of anymore I will add to this. I will say, personally it is one of my fav campaigns to run. 

I've been running the campaign solo and I had the party start out by playing Storm King's Thunder. After the party is defeated by a party of Orcs, I have them be sold to the Drow in "Out of the Abyss" so they can shift over to a different campaign. I had the party lose all track of time, they can only guess how long they've rested or been in the Underdark. I have two Wizards and a Monk on the campaign and they chose only one of the prisoners to help escape, the rest were released and chose their own path. I plan on having the party face the Demogorgon and treat it as if it was a Balrog from Lord of the Rings. Maybe have one of the wizards be taken by the demon and escape on his own and meet the party somewhere else. 

It's a fun campaign and I've purposely been dragging it out because I've been having a blast! 

Scarloc_Stormcall: Which homebrew module did you use for Gracklstugh?

Being a DM means learning how to spell & pronounce Menzoberranzan at will :-P 

One big thing to think about DM side is how the party is going to escape the Underdark. If you just bounce from place to place with no plan, you'll get to the end of the first section and have to either handwave a magical escape somehow, or figure it out then. More impactful to give them clues along the way about how they can get back to the surface. Lots of possibilities, and encourage the players to think about how they can get topside.

dont kill stool