I agree with Aeyoun's solution but you can obtain this achievement easily alone.
All you need is a second Xbox-Live account on your Xbox (with whom you are also friends on Xbox Live) and 2 Xbox-Controllers. Before you start going for this achievement be sure that you've started the game with the second account at least one time.
Once this is done log into your account (the one you want to get the achievement with) with the first controller at the dashboard. Do the same with the account from your friendlist with the second controller.
Start the game with the first controller and follow Aeyoun's instructions.