Look up a hops guide (google is your friend), and figure out which are best for bittering, flavoring and aroma. I would just have fun with the portions. Citra seems great for dry-hopping if you want to try that, as it has a need aroma profile.
This is me just making stuff up, so take with a grain of salt. To get some nice hoppiness, I would do a bittering with the Magnum and/or Columbus (depending on how bitter you like it, will be low to medium I figure), the Saaz for flavor, and then the Tettnang for aroma. Also find half a pound of another specialty grain if you can if you want to add a different depth to the ale. Others, enjoy a mildly hoppy amber!
In short, research the hops a little, is easy, and play with it.