Knots make lumps that show when the piece is framed and can pull through the fabric. Counted work is started and finished by running the thread under existing stitches instead.
The loop start
Use this whenever you stitch with an even number of strands. Cut one strand twice the length you want, fold it in half and thread the two cut ends through the needle so the loop is at the tail. Bring the needle up from the back, make the first half-stitch, and on the way back down pass the needle through the loop on the back. The thread is anchored with no knot and no tail to weave in. It is the neatest start there is and it works for the 2-strand stitching that most charts assume.
The waste knot
For an odd number of strands, or when you want to start away from other stitches, tie a knot in the end and take the needle down from the front about an inch away from where you will stitch, in the path of the coming stitches. Stitch toward the knot, covering the thread on the back as you go. When you reach the knot, cut it off; the tail is already held by the stitches.
Running under
If there is already stitching nearby, simply run the new thread under four or five stitches on the back before bringing it up. This is also how you finish: take the needle under several stitches on the back, going in the opposite direction to the way the thread was travelling, and cut close.
Length
Cut lengths of about 45 cm (18 in). Longer lengths twist and fray before they are used up; shorter ones mean more starts and ends. Let the needle dangle every so often to untwist the thread.
Keeping the back tidy
Do not carry a colour more than three or four stitches across bare fabric; finish it and start again instead. A flat back means a flat front, which matters most on light fabric and for pieces that will be framed under glass.