For beginner or quick scenes, i would suggest working modularly.
Make a couple of different trees, rocks, and clumps of grass. The easier you can tell them apart, the better. Save each as a Graphics symbol. (Or make each a new frame, if that makes sense)
Place them in various positions around your scene. Change the scale and rotation. Don't put two of the same right next to each other.
This way, you can focus on making each item look good, and your effort is multiplied.
Don't worry about reflections. Only shiny things have them, and unless you're trying to add a lake, you're fine. The trees need shadows... Think of them as 'fuzzy' spheres.
If you're really serious about getting it to look good, read up on composition.