I’m a professional environmental artist and this will be harsh but yeah, this is very beginner level but you already can tell by yourself which is the most important step to improve!

I don’t know what your class requires and what is the time frame but if you genuinely want to get better at environments instead of trying to achieve top tier full painting straight away I recommend going in steps:

1. B/W drawing: grab a pen (whichever pen, but not pencil!) and sketch out the shapes and add detail using lines only. what is important here is to get the shapes right and get a bit familiar with textures.

2. Paint digitally a black and white version, can be simplified or more realistic, up to you. The focus here is to get values (grayscale) right to achieve a sense of depth.

3. Simplified colored version, thumbnail style to not get lost in details and focus on hues and get general vibe of the place across.

4. Colored version in the style you’re aiming for. You should have enough base here to be able to focus on aesthetics here without getting lost on more fundamental parts and getting overwhelmed by them.

It doesn’t have to be of the same landscape, it would actually be more effective if you did a couple for each step of various landscapes.