Good day everyone, 

I've been running more theater of the mind style games recently (with a few visual aids), and am interested in hearing how others do it, and for things people enjoy in that style.

DMs, what are some important concepts to remember?

Players, what are elements you have enjoyed in theater of the mind style games?

From my experience so far:

• Don't overdo explanations, try to not talk as much as the DM, let imaginations take over
• Make sure players know initiative order 
• Be more free form with movement and positioning

Thanks in advance everyone.

Here is a good tip, there is a section in the DMG that suggests how many creatures should get caught in an AoE.

One of the best things about theatre of the mind is the interactive encounter building.  Without minis and a grid, players are not "restrained" to what is put in front of them, and neither is the DM (but really that's always the case).  It can really reward some "out of the box" player thinking.  Things can be approximate, especially with the ability to move within a creature's threatened space without provoking attacks of opportunity.  It allows the DM to "give" the players what they ask for/need.  Is there any cover in this room/cavern?  "Sure, there are some supplies stocked up to the left/right of you" or "Some of the stalagmites are big enough to provide half cover." Because forgetting to say something is quite a bit different than forgetting to draw/place something.

I usually keep some pictures handy for grand "shots" of locales, but rarely NPC's or creatures.  

Theatre of the mind encourages player mapping, at least after that session where they say "Ok, we leave the caves" and your response is "OK, how do you do that?" and the rest of the session is them devising a system of not going in circles, discovering places they missed, and some "random" encounters as they find their way out.  Only works once, and only works on newer players (usually, but there are those who "forget" their experiences).

I think my best tip is to pay attention to fight scenes and action scenes in movies and think about the tricks they use to keep the audience grounded with a good sense of where all the characters are in space.  Then see if you can do that using words.  How would you describe the elevator fight in Winter Soldier, blow-by-blow, to a blind friend?  Then try the hallway fight in Oldboy.  How would you describe the first fight/chase in Guardians of the Galaxy so that four PCs (Rocket, Groot, Gamora, and Quill) all knew where they were and where their individual objective was at any moment?  Now, try the antigravity fight in Inception.

Adding stuff to the room on a whim is fine, but make sure you describe it consistently.

Re-establish geography often.   "It's your turn.  The halfling just dove behind a waist-high stack of wooden crates off to your left.  The barbarian is chokeslamming an orc through a long wooden table on your right.  You're at the bar, trying to pull a third off of the wizard before it skewers him with a machete and, through the bar mirror, you see four more piling in behind you.  What do you do?"  If you're anyone at the table, you know which way your character is looking and which direction the new orcs are coming from, relative to them.  If you don't re-establish once in a while, players lose the thread.  Everyone becomes this weightless blob shooting at other weightless blobs floating in a grey space.

Not talking much is always good advice, but it means you should strive to describe things efficiently.  It doesn't mean "err on the side of not giving the players enough information."

As DM, draw your encounter area and place tokens on the map.  Then you have a visual to explain to them.  It is important for you to keep track of what is going on so you can describe it.

In general I recommend you have photos, sketches or dioramas to help you visualize what you need to describe to the players.