The best way to get over jet lag is to try to force yourself to be in the time zone you are entering.
For instance, going from NYC to London. London is 5 or 6 hours ahead of NYC. If taking an evening flight, it's better to try to sleep/rest on the plane if possible rather than stay up. By the time we landed, it was 2AM in NYC, but 8AM in London. I took an hour nap at the hotel before trying to push through the rest of the day to a 'normal' bed time in London time. Since I don't sleep well on planes, I probably only had 3 hours sleep that 1st day in London.
There are certain vitamins and such that people claim will help jet lag. Also, I find keeping hydrated is important. My eyes get really dry on long plane rides and that contributes to feeling tired.