If you want to work on hills (or really, just one hill), take the bike path that runs west from Shoal Creek, above the tracks, over to Far West Blvd, then ride down Far West, and then back up (if you really want to kill yourself on hills, Far West ends with a right turn into Ladera Norte, which is one of the steepest hills in town). Also, from the north end of Shoal Creek, you can go west on Steck and then south on Mesa to practice hills (Mesa has a 10% grade for a short pitch).

Here's one good place to explore: Ride with GPS has a bunch of routes that you can slice and dice.

Although I'm not a big fan of it (I'd rather be on the road), you might enjoy riding Walnut Creek Trail.

The Lime Creek loop up around Volente Beach is very popular with cyclists, and has little car traffic. It's very twisty-turny with short, steep hills.

Southwest Parkway is another popular road for cyclists with relatively little car traffic. Longer, shallower hills. Some people seem to drive their bikes out to it; one lap is about 12.5 miles.