Get a window seat so you can lean against the wall rather than against the person next to you.

Also, domestic first class seats are not as sleep-friendly as international business/first seats. If i'm going to sleep I won't try to upgrade a domestic redeye.

Some people like a bulkhead seat so they can stick their feet up on the wall and therefore find a greater variety of comfortable sleeping positions. Other people are grossed out that someone would stick their feet on the wall...

Don't plan any long drives or major activities the evening after the red-eye. My personal experience is that I feel OK until about 5:30 PM on a west coast/east coast redeye.