The colour of the plant's trichomes can give a good indication to the amount of THC and CBD and thus the optimum time to harvest. I recommend a jeweller's loupe or USB microscope.
Examples
Drying
The optimum air drying humidity is between 40 and 50% (RH). I keep around 20-22C. In the process of drying biologic processes continue inside of the buds and the chlorophyll is converted into glucose. Move a humidity sensor around your house to find a spot with good conditions. You can tell the buds are dry when the stems snap instead of bending when pressure is applied. The smell can also offer a clue as to how well-dried buds are, chlorophyll has a fresh-cut grass or banana-like smell
Note: under-dried/under-cured weed can induce a headache when smoked as a result of too much chlorophyll.
Curing
Once buds are dried they should be stored in an air-tight container preferably glass and "burped" (left open for 5 minutes a day) for a week or two