How To: Take a Cutting/Clone

Cloning Basics
Clones are, by definition, "a group of genetically identical cells descended from a single common ancestor." When cloning plants, roots are induced from a portion of the stem, root, or leaf. Clones or cuttings can be taken from a favorite plant and by repeating you can grow the strain continually and indefinitely.
Getting Started
Parts List:
Rockwool/Starter Cubes
Propagation Tray
Tray Insert
Humidity Dome
Cloning Gel
Cloning Solution
Heating Mat (Optional)
Razor Blade

The first thing you will need to do is condition the rockwool that you plan to plant the cuttings in. You will want to soak the rockwool in water that's pH has been adjusted to 5.5 overnight. This will neutralize the pH of the rockwool. This step is important because rockwool is very alkaline and putting a cutting into untreated rockwool could greatly reduce percentages of rooted clones. Most organic starter plugs are pre-soaked and do not need to be neutralized.
Now that your medium is prepared, you must select a plant to take cuttings from. Generally you will want to select the plant that is the healthiest and most vigorous of the group. Healthy mother plants will speed the rooting of the cuttings and increase your success rate, so choose wisely! Also, keep in mind that all the clones you take will display exactly the same characteristics of the mother plant so make sure you pick one with desired growth characteristics.
After selecting the best plant from the group, it's time to get all of your materials ready to take the clones. Put the black tray insert in the propagation tray and prepare a mixture of cloning solution according to the rates on the bottle. Make sure you have a sharp and clean razor blade handy.You may also want to set up a shot glass with enough cloning gel to dip your cuttings abut 1/2". 
Now select a portion of the plant to take the cutting from. Generally you want to select a branch or stem that has at least 2 or 3 sets of leaves. Locate a spot on the branch between a set of leaf nodes where your cut will be made. Leaf nodes are where the branches come out of the stem. Leave at least 1 set of nodes above the cut. Make a clean, neat, 45 degree slice with your razor blade. It is important that you do not damage the branch while handling. Now that the cut has been made you must work fast because time is against you. Remove the lower 1 or 2 sets of leaves leaving the upper set of leaves to be placed above the surface of the rockwool. To prevent an air bubble (embolism) from lodging in the stem where the cut is, immediately place in a container filled with your cloning gel. After you have dipped the clone in the gel place the cutting in the rockwool/starter cube immediately.
Place the cubes in the black tray insert spaced apart just enough so the leaves are not overlapping or touching then cover with a humidity dome. Keep in mind, the leaves may get moldy if they are laying on top of other leaves because of the high humidity in the dome.
Keep the dome on the cuttings with the vents closed. New cuttings need high humidty to root successfully. About once a day, you may want to lift the dome to allow fresh air circulation. At this time you may also want to mist the leaves with just water to keep the humidity up. The rockwool cubes should hold enough moisture to last several days without needing watered again. When lifinting the dome, check the moisture of the cubes and water as needed.
Once the cuttings begin to take root, they will not need as much humidity. However, you will want to gradually adjust the humidity within the dome so you don't shock the cuttings. Open the vents in the dome for a couple days before removing the dome entirely. Continue misting to keep some humidity, but gradually reduce the number of times you are spraying to allow the plants to be slowly weened off their high-humidity enviornment.
Congratulations! Your plant's genetics have just been copied!