I've always found that a little preparation goes a long way in getting the best rest possible. The process of taking off has some physical effects that can make you sleepy. When the plane disconnects from the airport terminal and its air system, there is no fresh air introduced into the cabin until the plane is airborne. This makes people very sleepy. The G forces introduced during take-off make you feel very heavy, so it's a good time to fall asleep.
Many people keep themselves alert until after the meal is served.
All the time spent waiting for your drink and meal has been wasted. Or better yet, bring your own snacks and bottled water. Sometimes falling and staying asleep are the main problems. Create a cocoon. I've become particularly fond of white-noise headphones.