Okay. The general idea is, two of the same will give you more of the same. Of course, putting them in different places will allow one to deal with different room affects, and so one can modify the in-room response with two. But getting this exactly right will involve measuring things. You can get it approximately right just by putting the two subwoofers on the middle of two adjacent walls of a rectangular room, or in two adjacent corners (for more output but less flat, generally). Here is a link to a page with links to various articles on subwoofer setup:
For one subwoofer, often a front corner is best, as it helps maximize output (and you only have one) and it being up front is usually not going to be a problem if you had to set the crossover a bit high due to inadequacies in main speakers. But the real best depends on careful measurements taken in your room. Next best is putting the subwoofer in the listening position and then crawling around on the floor and listening to (better would be measuring) bass and find where it sounds best, then put the subwoofer in that spot. You can read more about that at:
If you are not up for that, you can try it where you otherwise want to put it, and set it up with your receiver's automatic setup, and see how you like it. You might get lucky.