1. Mash Temperature
A great IPA, American or otherwise, is quite dry. American IPAs are very dry while English and Imperial IPAs have a bit more body, albeit for different reasons. When I first started brewing IPAs I was scared that I would make the beer too dry so I would mash at somewhere around 152 F, but the reality is that a lower temperature is required to get the appropriate level of dryness. 149 F is a much better temperature to mash at, but anywhere in the 148 - 151 F range should get you where you need to be.
2. Hops
Obviously, hops are the showcase of the IPA style and there are a myriad of factors to account for. Most brewing texts will tell you that the beer needs to be hop forward, but balanced by a supporting malt character, which is true, but it's not the whole story. There also needs to be a balance within the hop profile itself. The bitterness can't be too harsh or strong, otherwise the beer will be intensely grassy and unenjoyable. Too much hop flavor will drown out the supporting maltiness. Fortunately it's quite easy to achieve the proper balance with some alternatives to the traditional hopping schedule. For IPAs first wort hopping is great technique to get a smooth bitterness and a pleasant flavor/aroma component. Combined with late and dry hopping it creates a complex hop profile with several layers of depth to explore.
There are other topics that will help contribute to a great IPA, but I believe these two things are the keys. For a more in depth analysis of the IPA style check out IPA: Brewing Techniques, Recipes and the Evolution of India Pale Ale
. Cheers and happy brewing!
