IPAs are my favorite style! I make them every other batch or so. I rarely make IIPAs (too high ABV for me, as I drink at least 3-4 beers a night) but I love them too!
A couple of things that are important. You want them to finish pretty dry, so that they aren't cloying. I like to use less crystal malt than in my APAS, and use a very attenuative American ale yeast. Firm bittering at 60 minutes, with plenty of flavor/aroma hops at 15, 10, 5, and flame out make a nice IPA. Simple sugars may help keep the beer from finishing at a too-high FG, especially with extract making up the bulk of the fermentables.
A simple grain bill, say:
6 lbs Extra Light Dry Extract
2 lbs Vienna Malt (3.5 SRM)
8.00 oz Cara-Pils/Dextrine
8.0 oz Caramel/Crystal Malt 40L
for an OG of 1.066 or so. I'd use no more than 1 pound crystal total in a 5 gallon IPA, and you could even go with much less or none.
For hopping, something simple like:
1.00 oz Centennial [9.60 %] (60 min)
1.00 oz Centennial [9.60 %] (15 min)
1.00 oz Centennial [9.60 %] (5 min)
1.00 oz Centennial [9.60 %] (1 min)
1.00 oz Centennial [9.60 %] (Dry Hop 7 days)
That would give you a beer much like Bell's Two Hearted, an easy drinking IPA.
You could keep a similar grain bill, and maybe subbing a pound of corn sugar for some of the extract, and change up the hopping, and have a totally different beer. Some of the best IPAs I make are just base malt and a few ounces of something else, like biscuit malt, amber malt, etc.
For IIPAs, it's important to use sugar in place of some of the extract to keep the beer from becoming cloyingly thick and sweet. For an IIPA, target an OG of 1.080 and about 70-80 IBUs with lots and lots of late hops additions.
Some hops go together extremely well- simcoe/amarillo for one. But I also love centennial/cascade, chinook/centennial/cascade, and columbus/centennial for IPAs.
