The moment cannabis plants are ready for harvest, according to the great kudos of growing, is pretty short. While commercial growers often have to resort to mechanical trimmers to process lots of plants in a short period of time, home growers can enjoy harvesting by hand. Some connoisseurs even claim that hand trimmed marijuana tastes better.
For each plant you might need several different cutting devices with different size and precision - though in indoor bred plants a decent, sharp trimmer will do the trick. A good trimmer could be recognised by extremely sharp edges, as you want to cut the branches, not crush them. It should not be too big, as separating flowers from leaves is quite a delicate business and too bulky scissors might make it difficult.
Some of the cheaper scissors and trimmers loose their sharpness after processing a few cannabis plants. That is a normal tear and wear and should be taken into account - best prepare at least a couple of those if you are having your eye on a bigger crop.