First, let's define three important terms- Node, Auxiliary Shoot, and Terminal Shoot. A Node is an intersection on the stem of a branch where new branches can emerge. Sometimes they come in opposing pairs, and sometimes they appear individually. The branches that emerge from these Nodes are called Auxiliary Shoots. A Terminal Shoot is the top of the branch where the plant is mostly growing from- where it gains length. This can be casually referred to as the "Main Grow Shoot." In some strains, branching occurs from the Nodes without any external stimulation, but in others, the Terminal Shoot must be clipped in order to stimulate branching from the Nodes.
When clones are taken, branches are being cut off of the mother plant. The questions that arise are how much to cut, and what condition the branch should be in before it is considered a suitable clone.
Theoretically, any cutting with a grow shoot can root, even if that shoot is a tiny immature Auxiliary Shoot coming out of a node when the cutting has no Terminal Shoot. However, smaller less-healthy cuttings have a hard time rooting in comparison to taller beefier ones, and Auxiliary Shoots grow out sideways and can take a while to start growing.
On average, clones should be 6-7" tall, and 1/2-1" of that should be submerged below the surface of the medium. Cuttings should ideally have a nice healthy Terminal Shoot and at least one Node below that for best results. More than one Node below the Terminal Shoot is okay too, but no Nodes should be at or below the surface of the medium.
All the leaves on the cutting are best off being trimmed back just a bit so adjacent clones in a shared tray won't overlap each other too much. This is shown in the image above. Overlapping leaves can lower the survival rate of less vigorous cuttings.
That's the introduction for cutting a good cannabis clone. You can read more in my book, Marijuana Propagation, which can be ordered by emailing me from the contact page of this website.