I started watching the show, got like 3 or 4 episodes in, stopped and finished the entire first book, then finished the first season. Ending up reading all the books before season 2 then read Dance of Dragons about a year after it released (so before season 4?).

I plan on watching the show as scheduled as well. While I admire the restraint of book readers who want to stay pure until all the books come out, the problem with that is it's going to be EXTREMELY difficult to stay away from ALL spoilers until the seventh book comes out. With the cultural impact the show has, there's no way you can stay away from some sort of spoiler, even if you're diligent in staying off social media. If, say, Daenerys ends up with a heroes' death at the end of it all, then there's gonna be a shit ton of Daenerys shirts and merch at Hot Topic and Barnes and Amazon and whatever, spoiling the shit outta it.

I don't think it's worth attempting to stay away from the cultural zeitgeist for YEARS so you can find out where the show diverged from the books just to have some loud schmuck at a bar spoiling it a week after the finale airs.