Place the speaker symmmetrically, so the sound of the speaker reaches both ears at the same time.
Make sure that the distance between the speakers is at least 1.5 meters (~5 feet).

Do not place the speakers too close to a corner or wall. The distance to the rear wall (A) should be at least 20cm (~8''), 30cm (~12'') is better. You can play around with this for the optimum base.
B, or to the side wall should be at least 50cm(~19.5''), preferably more. The reflections of sound waves can be really annoying!

To tackle reflections, put something in between the reflecting point. To find this, slide a mirror over the wall, until you can see the speaker from you listening position in the mirror.

You can use audio panels, or something else: plants! Natural deflectors and absorbers of sound, and they give your place a nice feel.

Pretty obvious, but: do not place anything in between you and the speakers. Works really well!

Toe-in, toe-out, no toe, this all sounds complicated. But, its very simple! Just stick with symmetry, and angle the speakers so that they "cross" behind your head. Just as in the picture above. This helps to make the music more clear, as the higher notes have a direct traveling route to your ears.

Play around! Just place the speakers somewhere, and listen to a piece of music you love. Then put them somewhere else, and play the same piece again, and see what you can accomplish! If you really want to geek out on this subject: