I like unusual shirts and recently took it upon myself and my wife's sewing machine to start making my own shirts.
I ran into this rayon challis in the fabric store and decided I should have a tropical shirt of it. Converting my pattern to accommodate what I've heard about rayon challis involved turning the side seams and arm seams into french seams (after adding to the seam allowance on the pattern).
Surprisingly, it fits perfectly. It's not perfect by any means, but it's the first shirt of this fabric type that I've ever owned.
The biggest thing is to not be afraid of mistakes in my opinion. You will learn more about how constructions go together by doing them, making mistakes, reevaluating your mental model, and fixing those mistakes than you will by paralyzing yourself with fear.
Find a reasonable first pattern and make it several times. Then find a second pattern that takes skills from the first and adds others. In this way, you grow your skill set to accomplish the things you want to do.
Once you reach that point, try different materials. Learn about how different materials need to be finished, and use that knowledge to modify the patterns you already know. French seams are an excellent tool for this.
At this point, the world is your oyster. I'm currently working my way through a few new patterns, and a wild variety of fabrics. It's very satisfying, and I hope you enjoy it as much as I am.
This was my fourth shirt, but I recently posted my ninth. I've come a long way, and I still make a bunch of little dumb mistakes. It's fine, it has never ruined one of my shirts.
Oh and one more thing! When you buy a pattern many will be printed on tissue paper, and will have the lines printed for ever available size. It's expensive, but I have grown to love swedish tracing paper. It's not actually "paper", and the idea is that you trace your intended size lines of a pattern onto it, cut the panels out of the swedish tracing paper, and now you have a more durable way to repeat the exact same sewing pattern with whatever fabric you find yourself with. By doing this, you can keep the purchased tissue pattern as an archive. Maybe you need to retrace something eventually, or maybe you want to make the same thing in a different size one day. Regardless of why, you can't do that if you cut your intended size out of the tissue pattern.