It's a pretty vague question and depends on a few variables - how you're training now, your height, weight, and general fat condition (pudgy, kinda lean, already ripped, etc.), how you're currently eating, etc.
Generally speaking, that's not a whole lot of weight to drop in that long amount of time. If it's for a specific weigh-in or something, you could probably drop most of that in just a week, or a few days, by manipulating carbs and water (like fighters or lifters before a match or meet). But that's a temporary "solution."
If you're looking to drop 12 pounds of fat, again it depends on a bit, but lift heavy (to maintain muscle and strength), do some kind of cardio several days a week, and fine-tune the nutrition (most likely drop carbs a bunch and drop calories a bit).