What you need: sewing needle
Thread (I use 100% spun polyester Singer thread)
Hair weft clips (I got mine from Sally's Beauty Supply)
And hair extensions
Step 1: Thread Your Needle & Align Your Clip
It's easiest to do the ends of the weft first. My thread was about a foot long and was plenty.
Step 2: Attach & the First Knot
Start sewing through the hole of the clip that's on the end of the extension. When pulling the thread through, stop at the midway point, separate the two threads and have the needle be pulled through there to create a knot. This will prevent the thread from going through completely and adds support for the clip to stay in place.
Step 3: Securing the Rest of the Clip
After sewing the first hole two or three times, go through the teeth of the clip in the centre, pushing the needle through the weft and repeat twice or three times. When you're comfortable it is secure move on to the last hole. Repeat the same actions.
When your comfortable with the security of the last hole, I find it safe to go through each hole once more. To do this, go back to do another loop in the middle and through the first hole.
Step 4: Tie It Off
When you redo the first hole, cut the string off half way between your needle and the clip. Separate the two strings of thread and knot them at the base of the extension. I usually do a double knot, just to be safe.
Tada! Your extensions now have clips!