Most of the achievements in Gears of War 2 feel like they'll come naturally over the course of your time with the game. After playing through the game on Hardcore, I was left with close to 500 points. After spending some time playing splitscreen matches against an empty controller, I got that number up to just over 500. You're given plenty of opportunities to use weapons like the flamethrower and minigun in single-player, so racking up 30 kills each with those won't be a problem.
Playing against an empty controller in splitscreen mode can be handy, however, if you want to quickly earn things like Crossed Swords, the achievement for winning 10 chainsaw duels. A stationary player will automatically start a duel if attacked with the chainsaw from the front, so set up a match with respawns (like Submission) and get it there. You can also play 10 quick games, one on each of the new maps, to get the Around the World, Again achievment.
But when it comes down to it, my ultimate recommendation is that you should just play the game normally your first time through. Then go back through with achievements in mind. The game's worth playing, achievements or otherwise, so don't rob yourself of the experience by sweating the points your first time through.