Get a 30x magnifying glass, or if youve got a microscope lying around, thats even better. If you prefer a sativa high then harvest when the trichs are cloudy. If you want a mix of sativa and indica high then chop at a 50/50 mix. If you want a narcotic, knock-you-on-yer-arse high then harvest when the trichomes are all amber. Harvesting too late will cause the THC to break down in the trichomes, leading to an inferior high.