The idea here is to scarify the stem of your cutting so that there is more area in which the cutting can have the opportunity to grow roots and therefore hopefully increase your rooting success rate. You will need a sharp razor blade and a flat surface to scarify your stem.
The first thing you do is cut your clone at a 45-degree angle; this will expose both the inner and outer area of the stem. Now lay your cutting on a flat surface. Visualize about an inch from the cut end and place your razor blade at this point.
Gently, and with the slightest pressure, push the blade to the end removing a fine outer layer of the stem. Don't be in a hurry - there is no going back. Gently scrape the stem with your blade until you can clearly see the internal tissue layers. You have just successfully scarified your cutting.
Now it is back to the regular cloning methods. Dip into your cloning gel or powder and place into rock wool, soil, water, peat pellet, or aero cloner. When dipping your stems into your preferred cloning solution, you will want to ensure that you get the very tip (remember the 45-degree angle cut) and the length, which you have scarred. I have used cloning powder for demonstration purposes so you can easily see where I have applied the powder to the cutting.
This last image shows a successfully rooted clone that has used this simple scarification method. As you can see there are roots that have emerged from the full length of the scarring and not just from the bottom. This will give your newly rooted plant a much better survival and initial growth rate.
This method is also very useful for hard to clone cuttings and woody cuts which do not take to rooting easily. It is also a good method to practice at all times and in general it greatly increases rooting success and shortens rooting time. Other tips that one can use for those stubborn cuttings are to cut the bottom of your stem into quadrants to expose more surface area. One could also scarify two or three sides of the stem as opposed to the one side illustrated here to really give an advantage to those stubborn cuttings that will just not take. Just remember when scarifying more than one surface it becomes crucial that removing too much material off any one surface will ensure failure.
Some plants which generally take around 8 to 10 days to root, once applying this method, it is not uncommon to have roots after 5 or 6 days.
One last tip, I like to soak my new cuts in a glass of cool tap water for 15-20 minutes before preparing them to root. The chlorine in the water will kill any bacteria present and the cool oxygen filled water will be absorbed by the plant, giving it lots of reserve strength to push out those roots.
Good luck and happy rooting!