Copying is always a really important way to learn. I think, it's best to take baby steps. Start by copying something and then change parts of it. Another important thing is to train your eyes. and really commit your surroundings to memory.
I'm terrible with things like buildings and nature, so when I go to the park, I look at 1 tree and try to see what makes the tree. Where are the lines, shadows, branches, leaves. Are there moss or parasitic plants on it? Then look at the groves in the park and see how each individual tree works together to become a forest. Obviously it'll take more than a day, but going out and having the experience, so that you can replicate it; Not necessarily perfectly, but give the reader the impression of it.
A shortcut (really good if you're in a hurry)
Copy images from google and use them as a base for drawing.