A long-tail cast on is a popular method of casting on as it produces an edge that is stretchy but not loose while being neat and even. This cast on produces the same result as if you had used the thumb method and then knitted one row.
The two sides of the cast on are noticeably different so you can decide which you want to be the outside of the garment.
You only need one needle for this cast on. Pull out a length of yarn that is long enough to cast on all the stitches required. Make a slip knot and place this on the needle. Hold the needle in your right hand and place your index finger on top of the slip knot to keep it in position. The long tail should hang from the front of the stitch and the working yarn from the back.
Pinch the thumb and forefinger of your left hand together and insert them between the two strands of yarn. Spread the thumb and finger apart so that the long tail hangs over your thumb and the working yarn hangs over your index finger.
Catch both strands of yarn and hold them against your palm with your fingers. Insert the needle up through the loop around your thumb.
Bring the needle over and around the strand in front of your index finger.
Bring the needle back out through the thumb loop and let the loop slide off your thumb.
Put your thumb behind the long tail and use it to stretch out the yarn and tighten the loop around the needle.
Repeat steps 2 to 6 until you have made the required number of stitches. The slip knot counts as the first stitch.
This long-tail cast on will form a row of neat and even stitches.