Pull out approximately 1-2 feet of yarn from your yarn ball. Form a loop with the tail end of your yarn, and cross the yarn to form an 'X' at the bottom of your loop.
Step2
Pinch the 'X' between your thumb and forefinger of your left hand. With your right hand, form a smaller loop with the strand of yarn that is still attached to the ball. Loop the smaller loop up through the first loop, then insert your pointer finger through the new loop created.
Step3
Slip the needle through the created loop, tighten by pulling down on the yarn strings.
Step4
For easy, detailed video instructions, check out this link on howcast. http://www.howcast.com/videos/444-How-To-Tie-a-Slip-Knot-For-Knitting