Since it has been observed that some yarns shrink after getting washed, so to avoid this, it is recommended to pre-wash them before use. By doing this, the yarn will not shrink even after you wash your hair.
Now the fun part begins as you need to separate sections of hair, and for this it is suggested that you use a comb to separate small sections of your hair where the yarn extensions will be used. Work on one section at a time, as it is much easier that way. Also clip the surrounding hair to stop them from getting in the way.
The next step is to cut the yarn; you need to cut two pieces of yarn. Make sure that one is twice the length of the other piece. Knot the short piece at the mid-point of the longer piece in a way that three strands hang down.
You now need to braid the yarn in the hair. Hold the yarn from the knot and then slip the knot end behind the area of the hair you want to braid. It is important to remember that you need to braid the yarn along with the hair. Once you finish braiding, tie a knot at the bottom.
Repeat this on the remaining hair, moving from one section to the next.