Firstly, I wouldn't call myself a designer either. I've studied it a bit on my own time, but I'm still a programmer at heart. So maybe take this advice with a grain of salt. :)
For the most part, I think I start with navigation. What does my project need to do, and how could I navigate the different parts of it most efficiently? Should there be a navbar with different options? Tabs? Sidebar menu? Modal dialogs? Etc.
From there, I think most things fall into place for me. The exact style and look of my projects tends to depend on the feel I want for the application itself, but if I'm at a total loss for how I want something to look, I tend to check out sites like behance, dribbble, or codrops for inspiration.