Baking holiday cookies can go from a labor of love to an exercise in frustration when your gingerbread men come out more bloated than a Macy's parade float. The problem is too much heat—but not at the baking stage, at the mixing stage: Your butter is too warm.
The solution: Keep your butter cool, right until baking. Butter starts to melt at 68°, and once that happens, its water-fat emulsion breaks and there's no getting it back. Cold, emulsified butter helps give baked goods structure by taking in air when mixed with sugar. For cookies, you want butter well below room temperature; between 50° and 65° is optimal. Cut the butter into chunks, and let it stand at room temperature to soften (nix the microwave idea entirely).
If the butter is still cold to the touch but spreadable, you can start creaming. Butter and sugar need only be mixed (or "creamed") for about 30 seconds—much longer and the butter warms up. Chill the dough for 20 to 30 minutes before you bake. Lastly, don't put the cookies on a hot pan. If you're working in batches, cool the used pan for a few minutes, then run it under cool water before reloading (don't do this while it's hot, though, or you'll risk warping the pan).