Invest in a Jewelers loupe, x30 magnification and a small LED, You want your trichromes to turn from Crystal clear and shiny to crystal clear and milky(not shiny anymore) thats your que to start the flush (if youre doing one) then when those trichromes become at least 5% amber, thats when you know you can begin harvesting.
The more amber trichromes you get the more ripe its gonna be, but also, the smoking experience will be heavy on the body. Whereas if the trichromes are more milky then y ou will get a high that is heavy on the head instead.
Trichromes look like tiny hairs with a bubble at the end, like mushrooms and their caps.
I hope this helped :) good luck