Apart from doing research on perspective, it might be good to use the sfumato technique - think about your backgrounds as a series of elements put behind one another - like a stage set. Draw the front pieces in more contrast and the more in the background a thing is, the less contrast it has (and it's also generally a bit bluer than the front things). It gives the image perspective depth without worrying about complicated perspective rules, as you can see in this image:
(It's also great practice to just speedpaint random sceneries that come to your mind, like this.)
It definitely improves with every time you draw it, don't worry 
I think my best quality is expressing atmosphere and generally creating images that catch people's eyes and give off some feeling.
My weakest point is definitely drawing humans. I don't mean anatomy (I draw anthro instead), but the fact that they are human. It's a psychological problem originating probably in the desire to make original stuff. When I draw a human face, I always have the feeling that someone else already uses this style. And the older the character is, the more distinguishing characteristics they need to have, the more this feeling increases. A lecturer from mineralogy department keeps asking me to draw a family for his presentation but I always have to decline and feel really bad about it. I don't know how to overcome this block...
One thing I have more or less overcome, and might help people with similar problems, is horrible laziness and impatience when drawing straight lines or paralel curved lines etc. I hated drawing interiors but love nature scenes and broken things like fallen skyscrapers, as you don't need a ruler for that. Then I found the amazing Manga Studio which allows you to draw along various rulers which are really easy to set up. This was drawn in a trial version and I can't wait to get enough money to get the full version!
