The most important factor in harvest is timing for peak THC production.
in order to do this you must observe the trichomes (or trichs), which is the technical name for the crystally bits that cover your leaves and calyxes (calyxes are the bud bits that the hairs grow out from)
There are three types of trichomes, and only one of them produces THC in high quantities. This is called the "capitated stalked trichome" meaning a trichome with a stalk and a head. i forget the name of the other two types of trichs because i don't really care about them, except that it is one of the low THC tirchomes that give white strains the snowy appearance, that's why i don't recommend growing white strains, although a lot of people seem to love them.
first, (unless you are able to move your plant without risk of damage) select a small side bud and clip it off at the stem. then take it out of the growroom and into natural (but not direct) light. aim for flat but bright light, like sunlight reflected off a white wall.
get your magnifying glass (30X jewelers loupe is good, and only about US$20 off the net) , and have a good look at the trichomes from the side-on. Look for the ones like this : ======() and observe the colour of the head (cannabinoid secretions) and wait till around 50% of the capitated stalked trichomes have turned colour from clear to milky/amber. this will give the best all round high.
If you prefer a stronger "body-stone" then wait till more of the trichs have turned colour as the ones which matured first will be breaking down THC into CBD which gives more of a body stone.
If you only like Uppy buzzes, and want to avoid a body stone, then harvest once maybe 20-30% of the trichs have turned colour.
the smoke harvested early or late will not be as potent as the plant harvested at the point of peak THC production.