Choosing the best time to harvest marijuana depends on many factors. Indoor growers will usually run a 12-14 week cycle. The harvest can be completely controlled by the lights. After a 4-6 week period, growers will usually decrease the lights to 12 hours a day causing the plant to begin flowering. The flowering process will then continue for a further 8-10 weeks and then it is time for harvesting the marijuana plant.
Outdoor growers however, will have less control. The time for the marijuana harvest will depend on the types of marijuana chosen by the grower as well as the sun. As the days get shorter, the flowering process will begin and usually 7-11 weeks after this its time to harvest the plant. The sun's position will vary greatly depending where you are situated in the world, so harvesting time will subsequently vary. Usually in the northern hemisphere, the harvest will occur between September and November.
The actual process of harvesting the plants just requires pulling it out and hanging it up with adequate ventilation. Generally the slower the drying the better the result.