The sub crawl. You place the subwoofer on top of your couch (your listening position) and you play test tones or some music with good sustained bass notes and you crawl around the room marking the locations that it sounds the best. There will be areas where you may not hear any bass (nulls), other areas where the bass will be reduced (dips) other areas where it sounds muddy or boomy (peaks). Hopefully, you'll find a couple of spots where it sounds really good. That's where you place your sub. It's also a good idea to have a dB meter with you during the sub-crawl test.
Often, the best place for a sub will look silly or out of place. That's where two subwoofers come into play. Depending where you place them, they can help smooth out those nulls, dips and peaks at your listening position (but won't eliminate them entirely). Fortunately, the Dayton is priced where multiple subs can be had under your budget.