One thing to try is to place the sub in the listening position and walk around the room while a low frequency test tone is playing. As you walk around the room, try and listen to where the bass response sounds the best. When you feel that you've found the spot, you should place the sub there.
The room resonant modes are excited by the subwoofer, generating peaks and nulls in the frequency response in the < 250-300 Hz area. Ideally, you'd like to have the flattest possible response, but that's no easy achievement, since you have to understand how the modes build up in the room and try to avoid sitting or placing the speaker in a null, for example.
IMHO, the quickest alternative is to put the sub in one of the front corners, where the coupling between sub and room is maximum, then get a parametric equalizer such as a BFD 1124P for $129 and tame the peaks. There are many threads here on how to do this. Search for "BFD".
Alternatively, moving the sub around certainly makes a difference, and combining this with the BFD is the best option IMO, but this will require some study of room modes and also probably a software that can give you the frequency response of the room, such as ETF5.
Tod - I started initially placing my SVS 25-31PCi within 3-1/2" x 3-1/2" from the front and right side wall.
After a week or so, I moved it out to its present location. 5" x 5-1/2" from the front wall & the right side wall respectively.
This placement, in my 20' x 30' w/10' high vaulted ceiling HT/family room garnered the smoothest overall response coupled with the usual sub-sonic floor, air, wall, window impact, encoded in the DVDs!!!