There are no hard and fast rules when it comes to hops. Any hop can be used for bittering, flavor and/or aroma. Some are better suited for different applications, however. A low alpha hop is probably not the best idea for a beer that needs a lot of IBU's simply because of the sheer volume of hop material that is required.
Here are a few recommendations to get you started. Everyone's tastes and palates are different, so please play around. This is in no way an inclusive list, but it's a few ideas for you.
Clean bittering hops:
Warrior, Magnum, Horizon
Sharp bittering hops (suited for an IPA):
Tropical fruit aroma/flavor:
Summit (but it can also taste like onions, so user beware)
East Kent Goldings
The flavor descriptors aren't as simple as I'm making them look either. For example, even though I consider Columbus a dank hop primarily, I still get pine and citrus from it. I also haven't branched out into too many noble-type hops as I don't brew too many traditional lagers. I'm sure there are others here who can give you a bit more guidance in those styles.
I am a big hophead, and one of the primary reasons I got into homebrewing was to explore the whole hoppy side of things. I strongly encourage you to experiment. If something sounds interesting, then buy a few ounces and brew a Pale Ale with it. There are a few less-common hop varieties that have become staples in my brewery (Caliente and Motueka in particular) because I gave them a trial run and fell in love with them.