lay it all out and rough cut it all, leaving extra all around. (do not cut around anything yet).
Tuck one side (on the shortest side).
Stretch one long wall and tuck in the direction you are stretching.
Stretch it, tuck it then cut on the back side and tuck the small peice.
Work your way along that wall stretching and tucking,and cutting.
You can then begin to cut around things as you get to them ALWAYS STRETCHING 1st, otherwise you will leave a hole or gap somewhere.
When you are done go back to the wall you were bracing from and cut it.
Then repeat all of the above for the other two walls.

Disclaimer:
I used to lay carpet, but if any of this cause something to fuck up, I dont excist and didnt suggest anything.

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Love...the slowest form of suicide.