Here are a few tips, but you can search the forums and find answers from more knowledgable people than me:
1) Start with the sub in the corner were it will give the best bass. If too boomy, start moving it along the long wall of your room (assuming mains are on short wall) until it sounds good.
2) An Energy recommended "trick" is to put the sub in your primary listening position (that's right, put it on the floor where you sit). Now, walk around the room till the bass sounds the best. Note where you are standing when the bass sounds the best, then move the sub to that location. Then move around a bit to tweak.
3) The encore8 is rear ported, so make sure you have at least 6" of room behind the sub.
4) If you can't get the clarity you like with just position alone (quite likely), you may need some accoustic treatments targeting bass frequencies. There are a number of foam corner treatments and 4" thick panels that do not cost that much (and again, there are those that cost a fortune). Instructions for making your own at the cost of about $40 a panel can be found in numerous places including http://www.ethanwiner.com/basstrap.html