In general its hard to give critique on pieces like this because, at this stage is quite self-explanatory. Its all about fundamentals.
Not sure if you follow cubebrush (owner of this site) youtube channel, but do check this video
If you are going into landscapes then I suggest checking out this video
It helps tremendously for
1. Setting up your scene
2. Concepting out ideas
3. Focusing on the overall feel of the piece
4. Composition / Placement of the scene
After you feel quite confident with getting your value/image to read well, start experiment with colors. For now, take things in small bite-size, such as maybe focusing on how to paint a tree for example, or how to paint a rock, or how to make a rock read with just 2 values.
And don't be afraid of using reference or even getting out there to draw whats in nature. The best thing to do is to start drawing the subjects you want to draw. Eventually you will be able to do them from your imagination.
Overall this is how I would go about doing it. Again this is my own take. It has its own set of problems since I am still learning, but I like to keep things simple.
And one more video suggestion on How to Study
If you are just starting out though, just setup that drawing habit. Don't worry about too much technical issues yet. Because its easy to stop drawing if you're having a hard time, so best to start drawing your interests, and eventually introduce technical learning (techniques, how to color, perspective etc.) in your workflow/learning path.
Cheers!