Hops are where the fun and experimentation in IPA brewing really lies. There are no real limits on what you can go for here but some general rules of thumb would be; oily, high alpha hops work great. Basically, you want a big aroma in the packet if you expect to get a big aroma in the finished beer. Hops with similar traits work well together
Experimentation is key here as different palates will pick out different flavours in certain hop varieties. Play with hops until you have a good feel of which varieties match, which varieties clash, and which varieties contrast and then you will have a good understanding of hop combinations to use.