Have you ever really looked at the Long-Tail Cast On? It is such a versatile method, that it is worth a second look. (If you are familiar with the technique skip straight to the What is going on? paragraph.)
Try an experiment and tie two colours together one to be the tail yarn and the other the stitch yarn and look at the function of the two different yarns!
How about doubling the tail yarn for super-elastic hard working edges, such as sock tops? This automatically strengthens the edge and prevents the stitches from snuggling as close together as usual and gives a more elastic edge. Have fun, play with your stitches!
Long-tail (Continental) Cast On
If learning only one cast-on method, this would be the one I would recommend. It forms an excellent, general purpose edge. It is known by a variety of names, and it forms the basis of many other more elaborate cast-on edges, which become easier to follow once this one is mastered.
You will need working yarn and a single needle.
Unwind a tail of yarn approximately 4 times the intended cast on edge length. Make a slip knot. Place the slip knot onto a needle and firm up the loop to gently fit the needle. Place the ball of working yarn out to your right.
*Hold the tail yarn out to the left with your left thumb above it. Make a loop in the yarn by dropping the tip of the thumb in a circular motion, first down away from you, back towards you and then up to its original position. There should now be a loop of yarn around the thumb (as it crosses the thumb it should look like the middle portion of an S). Slide the tip of the needle (holding the slip knot) up the side of the thumb into the loop. Leave the thumb in the loop.
With the right hand, throw the yarn leading to the ball around the needle as if to knit.
With the left thumb push the loop up and over the needle tip and extricate the thumb.
Whilst maintaining a gentle tension on the working yarn (leading to the ball), tighten the tail yarn. The yarn thrown around the needle should now look like a stitch.
You should feel a little resistance as the loop firms up underneath the needle.
Repeat from * for each stitch. The slipknot is also counted as a stitch.
What is going on?
The new stitches are formed by the working yarn (held on the right, leading to the ball) being thrown around the needle just as in regular knitting. These stitches form an edge because they are each being held by a loop of tail yarn around the base of each. The tension on the right-hand yarn controls the firmness of the new stitches; keep this gentle but firm, similar to your usual knitting tension. If your cast-on stitches are habitually too tight, then practice relaxing the tension on this yarn as you cast-on. The newly cast-on stiches should be only fractionally more difficult to work than your regular mid project stitches.
The spacing of the stitches is controlled by the tail yarn (held to the left). The elasticity of the edge is directly linked to how closely the stitches are placed together on the needle. For socks, extreme edge elasticity is required to permit the sock to stretch around the heel. With practice it is possible to space the new stitches further apart than might be usual. The secret to controlling the spacing is to keep the left hand yarn at 90 degrees or less away from the needle (measured from the tip). As you tighten the left hand yarn do not allow the stitch to slide very close to the preceding st.
After checking and counting your cast-on edge, cut off all but 6″ of any remaining yarn tail left over from casting on. Finding a knitter that has never launched forth on their knitting, only to find that they were working with the tail yarn, would be an Herculean task!
Other than for Tubular Cast-on, don’t use a larger-than-gauge needle size for regular casting on; this only creates elongated stitches but no extra distance between the adjacent stitches. The resulting edge is slightly looser, but only because everything is a little sloppy!