How can I get to sleep on a plane

look around the plane to see if there might be 2-3 seat that are unoccupied next to each other and ask the flight attendant if you can switch. done that many times. or, when you book your flight, choose a seat that's at the front of a section or next to emergency exits, they have more leg room.

For me it is a little easier if I am in the window seat because I can lean against the bulkhead.

Drink two bottles of nyquil

over the counter chemicals ;)