Ascents: If they aren't that long, just attack them. It's just easier that way.
Descents: Learn to spin. Ride the brake(s) when necessary. While you should probably learn how to fixie coast, don't make it a habit.
Sloppy habits: It's a myth that fg will make your pedaling "rounder". If you're not careful, you'll rest on the upstroke knowing the pedal will push your legs up and over. You'll immediately notice it on a geared bike. Working on spinning will help develop a rounder stroke and you can do that on any bike. Descents on a fixed gear make it easy to learn since you have to learn.
Extra long skids: Balls on the stem, weight forward and you can skid pretty far even when it's dry out.
Skipping: an even better skill to have than skidding.
Track standing: useful if you're riding on a velodrome or mountain biking or want to impress people that couldn't care less.
Enjoy!