Try to prepare a few days in advance. If flying west go to bed progressively later and get up later if possible. When going east do the opposite. When flying west try to get a flight that leaves in the afternoon so you don't have to get up early and push your body clock the wrong way. When going east get an early morning flight if possible.
If you want to sleep avoid caffeine and try to be in a completely darkened room. Alcohol may or may not help, its different for different people.