Do what I do. Don't worry about it. If you make something within key then cool, but usually (always) when I make something up without thinking of any rules, so to say, it ends up out of a lot of keys. Best thing I do in that case is just find somewhere it fits, things don't have to be perfect to work together, that's what makes the music history as cool as it does. Because a lot of people just say "if it sounds good, do it". Not that I have issues with keys and so forth, I just don't like to tame myself with my writing.