A speaker system from a projector viewpoint should be symmetrical relative to the listening position. Meaning where you will be sitting. There should a be Left and Right speaker 2ft minimum away from your screen and at tilted at 45 -60 degrees aiming at your ears, including the height and the capability of your room.
I assume you plan on getting a 5.1 system. Same left and right rules apply. The subwoofer speaker should be placed in between your left and right speaker aiming at you. Never against any object, another speaker or wall.
The center speaker in the center below your screen.
Left & Right Surround speakers should be placed accordingly to your listening/sitting position right above your head, to disperse the sound.
If you end up going 7.1 you will have to place your listening/sitting area 3-4 minimum away from a wall and place you Left and Right Back Speakers at the same height of the surround speaker yet behind your head and aiming at your ears.
When placing your set up, bring a friend and sit them where you will be sitting as a reference or place your chair.