I like to think I'm pretty good at drawing characters - because that's what I have the most practise doing. Expressions, body-language, character designs, etc.
My weak points are architecture, perspective and stuff like water and sound-effects. I haven't drawn them as much, and so I'm not as good at them - but I'm slowly getting better, because I've been practising a lot lately.
With stuff like architecture and environments, I find it helps to not think of them as "backgrounds". They're not just stuff to fill in the space around your characters; they're a setting that is part of the story. The environment can tell you just as much about the story as the characters can. Say you're drawing a spooky ghost story, and want to emphasise how creepy a place is - you can do that by creating an environment that is dark and weird and creepy-looking. Throw in some weird angles, draw houses that look worn down and kind of broken, throw some cobwebs or creepy-crawlies in there. Likewise, if you're drawing a story that's supposed to be upbeat and fun, use brighter colours and open landscapes and cozy-looking architecture. Let the setting become a character in the story.