Before playing a move, I like to think I pay attention to the following :
Is some piece of mine undefended ? If a few aren't, then I should bay a particular attention to them not being forkable, with anything (by a queen, mostly). If it is the case, I might decide playing something that safens this matter.
Is my king safe enough ? All checks my opponent can administer should be benign.
Is my move achieving something ? Better have a wrong plan than no plan at all.
What move am I expecting my opponent to play ? A handful of possible moves is fine, as long as it's not “well, anything, basically”. Ideally, I see how neither of these moves are a problem to me.
Tactics : Often enough, there is about one square of interest on which both players' pieces concentrate : is this square defended enough times, by the right pieces ? (i.e. defending with a rook and a queen a pawn that my opponent attacks with light pieces is not going to help) Is the checkmate I am defending from still not working ?
Of course, once I thought enough about all of these, I'd expect not to lose any game, but 4. and 5. still leave the door open to surprises if one doesn't read variations into enough depth, “how many is enough ?” still being an open question :·)