As seen in Simply Knitting
Use this tried-and-tested technique to lay your foundation stitches.
 Step 1Make a slip knot leaving a long tail, place it on the needle. Hold the needle in the right hand, pass the ball end of yarn over the index finger, under the middle finger, over the third finger. |
 Step 2Holding the tail end of the yarn in your left hand, wrap it around your thumb by bringing the needle across to the left. |
 Step 3Now insert the point of the needle through the loop from front to back. |
 Step 4Wind the ball end of yarn around the needle, going from left to right. |
 Step 5Gently pull the loop through the thumb loop, moving the thumb over the top of the needle, as shown. |
 Step 6After removing your thumb, tighten the loop by pulling the tail end of yarn. Repeat steps 2-6 until you have the required number of stitches on your needle. Here's what your needle should look like once you've applied the thumb method of casting on. You're now ready to embark on your first row. |