Sam Noyoun posted an Instructable with 10 ways to improve your night vision. Robert Bruce Thompson and Barbara Fritchman Thompson covered some of these techniques in Astronomy Hacks (including the pirate eye patch trick), but there are a few I hadn't heard of:
1. Protect your night vision
It takes approximately 30 minutes for the human eye to adapt to darkness. Protect your night vision: do not look directly at bright objects (for instance car headlights when driving).
10 ways to improve your natural night vision - Link
Robert Bruce Thompson, who has had a lot of experience looking at dim objects in dark places, says that only a red filter will work: green and blue won't do the trick. Robert also says that the elite forces and soviet special forces techniques don't work.