I normally don’t reply to posts, however, I felt I had to on this. The question “How am I going to be able to build better than this” is, for a lack of a better term, a difficult question to answer. I used to ask myself this multiple times when I started out building, and I still do to this day. The answer that I’ve found is that there is no answer if that makes sense. You’ll always be looking to improve your work on Roblox, up to the point where your PC can’t handle the number of parts, voxels, or triangles anymore. I’ve been building since 2016 and I still have a long ways to go before I can be satisfied, and I may never be satisfied with my work.
So, the ‘answer’ to your question, is to keep working and do more and more work. Perhaps, instead of using those free models I see in your picture, possibly search up on the webs “How to create a realistic tree in Roblox Studio”. Now, creating a realistic tree on Roblox will only get you so far, which is where you may want to learn Blender which is a ‘hobbyist’ software you can use for free. I’ve used it to create my trees and I hope to never stop using it for my work. Maybe now search up “How to create a realistic tree in Blender”, or, just start with the simplest of steps and create a low poly tree, that’s how I started.
If that doesn’t float your boat, I would suggest looking at other showcases on Roblox for inspiration or ideas. I do this all the time, and sometimes when you’re taking screenshots of someone else’s work and you go to recreate that yourself, whether in Blender or Roblox. You’ll have learned something new, you can now create that object and multiple variations of it, hopefully anyway. One thing I learned when building, is that you don’t have to make anything realistic, you should make it how YOU want as it’s your imagination and work. When you start creating something, and it may not look good, keep it and just continue to develop on it, and hopefully, in the end, it won’t look too bad.
I hope I was able to help with your question. I’m not quite qualified to answer this question as I’m not the best builder myself. All I can say is that you need to just keep building, get reference images from either other showcases or real-life images. Good luck!