Ableton Forum

Either like sketched out below, or should I place my desk in front of the window with monitors pointing out to the long end of the room, in a symmetric way?

They should be on the long wall, and in the middle - you'll have resonant bass frequencies popping up from your left speaker/corner wall combo which may, for the lower frequencies, either over-represent or cause phase-cancellation.
Keep an eye on your spectrum analyser and you can taper anything unusual though.
And get some heavy curtains.

The best practice to place your monitors is to have it in an equilateral trinagle with your head in such to not see the rear walls of the monitor only their faces and space between them at least 1,5m.
Put them so that the hights to be on the same line with your ears.
Place them on top of something spongy or on some standers for decoupling.
Enjoy.
Cheers

I shall try.

Place them symmetrically facing the long way down, i.e. where the window is, but don't place them right next to the wall/window, but some distance away. Also make sure that the distance from each speaker to the walls/ceiling/floor are not the same - i.e. Speaker A distance to long wall is not equal to distance to short wall is not equal to distance to ceiling is not equal to distance to floor. Same for speaker B. TO find the best location for the speakers in your room and for your listening position following the advice of the link Kev Herb posted. Also, get EQ Wizard (free) and a test mic (a cheap one like the $50 ECM8000 will do) and see what placements give you the flattest response.

Nearfields handbook (by Tannoy- not specific to Tannoy products though)

http://www.sweetwater.com/NearField/