Learn which ideas grab you, which ones you feel you could do justice, and which ones the world needs to see. Just get those ideas down on paper and explore them.
Sit down with your laptop, pen and paper, or vintage typewriter and start brainstorming ideas. You probably already have a few in the back of your head. If you don’t have any ideas yet, you’re lying. Where would we be if Vince Gilligan had forgotten to scribble down “Chemistry teacher cooks meth to pay for cancer treatments” in his idea journal?