Exactly as it says on the tin, just complete the campaign and bing.
The only thing I would say, is play the game on Hard - despite the name this campaign really isn't as long as you don't play stupid and run out into gunfire. The reason I say this is that you need to complete the game on Hard to unlock Tier 1 and Hardcore difficulties - and why add an extra playthrough if you don't have to!
Please comment if you down-vote so I know how to improve :)