Don't harvest too early. Wait until the buds change color (purple, blue, grey).
A big change of color in fall will occur (green flowers with white pistils will be dark purple with brown/orange/darker pistils, you can't miss it). Pistils will eventually fall. But look at the trichomes with a jeweller's 10x or 30x loupe TO BE SURE on a sample at home (or backwards binoculars real close). Early buds are smaller and less potent. Once dried, they can be much smaller (depends on strain too). Sometimes it looks ripe, smells ripe but you're wrong: the trichomes were in fact all clear!!! The buds could have become much bigger, more potent and tastier. Trichomes will change from clear to cloudy to amber. People usually harvest at 50/50 cloudy amber. The effect depends on the sativa/indica ratio but clear trichomes will give a lighter high and amber trichomes will give a more couchlock and potent high.