Write something at first; maybe use one of your partial ideas and really concentrate on making something small, but good. Now, put that away somewhere out of the way, but still accessible.
Now, write something else entirely. Maybe another small project. Keep going. Write more. Do a little writing each day, and in between, read stuff written for different audiences. Read MLK's "Letters from a Birmingham Jail." Read some sci-fi. Read a comic book. Read a boring, dry report about something. Absorb, then write again.
Now, after a month or so, maybe two, pull out the first thing you wrote. It will give you a good gauge of the progress you've made. And you might hate what you wrote, and that's OK, as long as you realize that the first thing you wrote is the floor, and you're only going to get better from that point on. Finally, plan! Sometimes creative genius can come out of the ether, but it's best to plan and not rely on that happening. Give yourself a destination and rough idea of how you'll get there. Then let the wind take you.