I'd recommend studying (real life) references and watching tutorials on the youtubes. Also Bob Ross it up.

You should try and treat it like character art; when we think of the basics of that we think of stuff like anatomy, figure drawing, etc. Environments can be the same; study the basics (even just shapes in perspective if you have to), study from life, copy masters. You can learn composition but composition is relative (aka once you learn the rules you can break them, just like with anatomy)

If you can learn to "characterize" backgrounds I think that might make it a lot more fun? Like having a set visual dictionary for shapes and overall background feel/mood as opposed to just copying realistically from life.

As for actual practicing, thumbnail paintings are a great wait to start; go right in with colour, make shapes, make compositions-- or heck they can just be black and white. Don't fret about details, those can come later.

also maybe think about graphic shapes and how we relate to them; IE: you can most likely just draw an egg with a rectangle sticking out of it at the bottom and have it read as a tree, the same way we can recognize a simple ":)" as a face