Best setup for 5.1 speakers in room
Yes there are guidelines for how to place the speakers. E.g. here is a Dolby 5.1 placement guide. But the short answer is A, B, C, F, and E in your diagram, if you have to pick from those exact spots.

Also note that some higher-end stereos have a calibration feature that will use a microphone and test tones to detect the placement of each individual speaker, and can correct for some non-optimal placements. If you have a stereo that is capable of that you can rely on that to fix some problems. Few people are lucky enough to have a room 100% dedicated to a home theater, so it is common to have non-optimal placement due to other factors (doors, other furniture, etc).