Things to avoid.

You've just got to do it, basically - smoke, grass, textures, I can manage. I've had problems with painting water, specifically the sea, for a while - have taken a holiday from it so I can come back with a fresh eye: I could do it once, but just a few paintings in which I made a pig's ear of it chipped away at my confidence. I'm working on a sea picture now, as it happens, with a bit of helpful land to disguise things if the water looks wrong (I know it won't disguise anything, really.... I'm lying to myself). I always used to hide hands and feet - but realized that this was cowardly: unlike you, I don't draw or paint figures very often, so am no expert - but I think I can do it now. The thing is not to make them grossly disproportionate - generally, beginners draw/paint them far too small: I wonder why that is, but I've noticed it often. Back to the sea again - you can develop a bit of a psychological hang-up about specific things, particularly if you've had a couple of disasters with them. The answer nearly always lies in the sketch-book - working out your issues there solves most problems. I drew the hands I couldn't draw until - I could draw them. And what you can draw, you can paint.