What are the things that are most important to you in deciding how pleased you are with what you have written?
I guess it takes practice - and I've had A LOT OF THAT - but when you cast your mind over something that you've just finished writing it speaks to you about how good it is... and about how good it can be. It isn't something like a checklist, a bullet list of things I "look for" when I look back over a piece of writing - but it's an instinct, and sometimes it isn't even specific enough for me, the writer, it's just "there may be a problem with this, FIX IT". But there are times - and these are the times that writers live for - when you are looking at something that just came out of your head, that you just typed on the screen, and your own words raise hackles... and you have no idea where that thing you've just written actually came from, you just know it's there, and it's close to perfect. Sometimes the story takes care of itself and all you can do is sit back and take it, take whatever it dishes out. But if you really want something particular then it boils down to just a couple of things - is there "JUST ENOUGH" there (i.e. is there overindulgent purple prose that needs to be slashed out, as in too much, or are you telegraphing things that you need to explain (because YOU already know stuff and you didn't pause to remember that your reader doesn't), as in, too little); that, and did you get your voice right. Every character has their own voice. They should speak to the reader in THAT voice, not yours. If you can hit those two brass rings... you're already halfway to done.