I'm going off of what other people said, also I don't understand why people think they can watch tutorials and think they suddenly are an expert.
You need to actually do it, not only one. MULTIPLE times, and every time the product will get better.
Like others said, practice. I've joined in July of 2010 and this was my first build:
(Ive literally built it in front of a building I'm working on right now but whatever, I remade this to the best of my memory and I DO remember building it on the slopes, and I put as many trees as I could before exceeding the BL Demo brick limit)
My point I am trying to make is, practice makes you improve, just compare my work now to that image above.
I have been practicing building for several hours every day for years, and sometimes full days even. Not because I wanted to be the best builder, but I just liked building and I got such a kick out of it, and I still do today. I love creating in this game, even tho the engine limits are infuriating at times.
But yeah, this is practically an art form, and ALL art forms need practice to gain improvement.