Walk around the drums while the drummer is playing the kit. Be sure the drummer is playing at the same intensity he will be playing when the drums are being recorded, as this can dramatically affect the way his drums sound in the room.
Listen for spots in the room where the drum set sounds better or worse and make notes as you do so. Use a ladder, if available, to listen to the drums at different heights. Ear level might not always yield the best placement. Some good starting points are 6 to 10 feet above and directly in front of the kit, in front of the drum kit at ear level or directly above the drummer's head.
Plug your microphone into a recording device and listen to the output in the control room once you've found some "sweet spots" to place the microphone. While you are listening to what the microphone is picking up in the control room, have an assistant move the microphone from one spot to the next so you can determine which position yields the best drum sound.