Do it by all means, but don't rearrange the furniture or put your feet on anything anyone else has to touch. Also, if you're going to take your shoes off then your socks must stay on and you must give an honest appraisal of the, erm, perfume they are emitting. If there's even a tiny whiff then your shoes go back on immediately.

If you're going to set an alarm then do it through your headphones, or drop a tip to one of the staff to wake you up when the flight is called.

If you get woken up by people moving or talking around you then that's your problem, not theirs, so don't give people dirty looks.

If you regularly have trouble sleep on long haul flights then I'd suggest going to your GP and asking for something to help. If I can't sleep on a flight it's usually because of tension that results from so much going on around me so I find that a mild hypnotic like Zopiclone knocks just enough tension out of me to help the fatigue take over. Valium works too but can leave you with a bit of a hangover when you wake, whereas Zopiclone is quite short-acting.