Herb it up
People are always telling you to eat more greens. Try starting with Calea zacatechichi, better known as the "dream herb." Used by the Chontal Indians of Mexico to induce mild hallucinogenic trips, the dream herb is one of the few (legal) herbs that might increase vivid-dream frequency. It's pretty easy to find in tea form, although you probably shouldn't have a tea party with it, unless you want that party to end up as a sleepover. Other herbs, like mugwort and Huperzine A, get a lot of hype in the lucid-dream world, but there's not much evidence to corroborate these claims.