I have never had any luck with any dose of melatonin. It does not help me fall asleep, become lucid, help remember dreams, or increase vividness.

B6 does, though. I take it infrequently (high doses of B6 constantly can fuck your shit up), about every month. Usually 2 pills, a 200mg dose, during a wake-back-to-bed (so, 2-3 hours before I normally get up). Dreams end up more vivid and more easily remembered.