While it's possible to play BREAK!! combats entirely within the theater of the mind, I highly recommend you use some sort of physical (or digital, if your games are played online) map while doing so. Having a map to reference helps everyone at the table re-focus if something else catches their attention and can help prompt them to come up with things like stunts, tricks, or other stratagems.
This is especially true for important Guardian Encounters! While you can use the standard battlefield map for most smaller scale encounters, having a special map for big fights can really add a lot.
Don't fret though! Drawing one is actually much easier to do than it might seem. While the rulebook has some really gorgeous looking examples thanks to Grey's spectacular art, you can honestly get away with much simpler ones that just about anyone can make.
A good way to think of it is that BREAK!! maps, whether it be Region Maps, Adventure Sites, or Battlefields, are all about nodes.
Here's a quick mock-up to show what I mean. I made this in a few minutes in MS Paint, but in my home game I'd likely have doodled it on some index cards or on a dry-wash mat:
This battlefield is intended for a sort of ambush in a cave. There is likely a large, intimidating guardian on the path or near the exit, while some spell casters or foes with missile attacks are perched on the ledges, ready to rain whatever dangerous annoyances they have down on the party.
The important spots on the battlefield are clearly labeled and any conditions that apply to them listed as well. The lines connecting the points make it clear how players are able to move, and some notes at the top add any considerations that apply to the entire thing. All you need are some minis or tokens or other things to mark where everyone is and you're ready to go. The party has a lot of choices here to - do they try to climb to the ledges? Barrel through the main threat? Turn around and get the heck out of dodge?
And that's really all there is to it. Like all things with GM Prep, try not to stress too much and have fun!
Some Farewell Tips:
- Don't worry about detailing everything. Keeping things simple and a little open works well with how BREAK!!'s rules flow. As an example, you can just say "debris is scattered across the floor" without being too specific. It it may prompt a player to ask if there is anything sharp or big enough to throw as a weapon, or things like that, getting them to further consider the battlefield in their actions.
- Keeping the opponents the battlefield is intended for in mind is obvious, but don't forget to consider the fun things about your adventure site as well. A fire temple might have over-heated areas with the dangerous condition, magic forests might have precarious areas swarming with writhing vines, magic polluted facilities might have status ailment causing gunk in certain spots, and so forth.
- You can make a few quick template maps and reskin them for different adventure sites, I won't tell anyone.