I've never used a decoy, but I've heard of people who have with success. At this time of year, either a buck or doe decoy should work. The thing with a decoy is, a deer (like duck decoys) must be passing by in order to see it, so if there are no deer passing by, it won't do any good.
If you can try calling the deer and they see the decoy, then it might draw them in for a shot.