I generally look at a game's list when I first start playing, and if they're well thought-out, by my definitions (and these are easy to see, i.e. the ones for RE 5 or maybe GoW 2 or something like that), then I'll go for them. I also like the ones in Sonic's Ultimate Genesis Collection. Good way to get me to keep playing some old games that I might not put too much play time into otherwise.
But when they're not very good (i.e. X-Blades, 50-Cent: BotS, etc), I don't try for them. Play the game once, get the ones I can, don't worry about getting more.
And here's a debate I'd like to hear some opinions on- what do you all think about games where the bulk of achievements come from playing on the hardest difficulty? EA Sports is bad about that, like on NCAA March Madness 09, for instance, just about everything is only for the two highest difficulties. Annoyed me in that. But then, on the other hand, I don't really mind it in COD: WaW. Game Informer called it out as a bad, bad idea in a recent article, not sure where I am on that one.
Anyway, I suck at a lot of stuff. My most notable achievement is being a willing punching bag online in various versions of SF.