Well i was told by a friend of mine i would be better seeing the first x men movie first so i knew who was who plus i think there might be some reference to the first movie.
Hiya:
I can't say that you'll actually 'miss' much but if you watch the first one soon before the second one, you'll appreciate the story line a lot more as well as the stunts. Having said that, if you've been reading the comics, you'll have the gist of things anyway. Cheers.
I dont think you need to have seen the first one, but it would help. I went with my girlfriend and she hadnt seen the first film. Its relatively clear who the good/bad guys are and where it isnt clear thats because its not meant to be.