When you have more than four stitches between colour changes you should weave the yarn not in use under and over the stitches on the reverse. This technique is called weaving. As with stranding, you can weave using one or two hands.
If you leave loops of yarn that are longer than four stitches at the back of the fabric they can catch and snag so it is a sensible move to weave the strands into the stitches as you work. Weave the yarn in every second or third stitch.
Weaving one-handed on the knit side:
Work to the point where the second colour needs to be woven in – this should be every two or three stitches.
Bring the second colour up from under the one in use and over the right-hand needle and your left forefinger from right to left.
Knit the stitch using the right-hand needle, dropping the stitch and the carried yarn from the left-hand needle. Hold the non-working yarn in place at the back of the work, using your left forefinger, and continue to knit using the first colour.
Weaving one-handed on the purl side:
Work to the point where the second colour needs to be woven in. Bring the non-working yarn up from under the yarn in use and around the right-hand needle from right to left. Keep it in place at the front of the fabric with your left thumb. Purl the next stitch.
Work to the next colour change using your left hand to wrap the yarn around the right-hand needle.
At the next colour change the new yarn becomes the working yarn and is brought over the non-working yarn to begin the next set of colour stitches using the right hand. On the back of the fabric you will see the loops of yarn held neatly in place.
Weaving in the yarn on the reverse also helps to keep the tension even.