I started using one hop at a time for dry hopping kits so that I could see what each one was like. M&S also used to sell a good range of single hop beers (not sure if they still do as I haven't been for a while).
I now know which ones I prefer and which combinations may work so look at recipes others have done or clone recipes of commercial beers I like to try and get the ratios of the hops right. However it's still a lot of fun just experimenting if you're not after a particular result!