Probably a pretty simple rule of thumb is:
Are you asking a totally new question? Or did you totally stuff up expressing your previous question, and want to ask roughly the same thing better? If it's the former, ask a new question. Otherwise you should probably revise.
You could consider flagging your post for moderator attention and asking for it to be closed as unclear temporarily whilst you edit it, to save people - including yourself - the trouble of poor answers accumulating whilst it's not clear enough. (I think? I haven't done this before but it seems like a pretty reasonable case for moderator intervention & assistance.)
You can also ask chat for help in better communicating your intentions on the question. You could also ask meta, maybe, but I'm not sure how that'd work out. From the concerns that culminated in the meta Q The role of chat at RPG Stack Exchange, if you seek help in chat, then when you make the revision, please link back to the conversation (e.g. a permalink to a chat message) somehow - the edit summary might be the best place for that, since it doesn't necessarily belong in either the question itself or the comments. (The same meta Q mentions that meta is the place to discuss the site, but also acknowledges chat is great at the kind of extended discussion this kind of thing might require, so I'd err toward using chat myself.)
Your edit might invalidate certain answers so that they're no longer answering the new question. The basic policy for handling that situation is here: What do we do with answers made obsolete by a question change? — since they're no longer answering the question, flag them accordingly, maybe leave a comment explaining the situation for the author and for people who will respond to your flag. The unofficial policy is also probably try to avoid creating this kind of situation by asking clearly in the first place, but sometimes this happens.
