Pick a seat where you will be comfortable. Many people prefer the window seat for sleeping because you can lean against the side of the plane.
Place the earplugs in your ears as the sound of flying can produce a lot of ambient noise that makes it hard to fall asleep.
Recline back in your seat to a comfortable angle and place your blanket over your lap to keep you warm. The seats in first or business class will recline further back than seats in coach.
Place your travel pillow behind your neck so that your head is supported if it falls to either side.
Place the eye mask over your eyes to block out unwanted light.