While there aren't any solid rules regarding signing with your baby, I've had enough experience signing with my own child that I can pass along some helpful hints.
Be consistent. Use the sign the same way every time for the same action or object. This will help your baby become familiar with the sign and she will be able to sign it back to you sooner.

Be happy. Frowning and bored voices will not make a baby eager to sign.

Be open to interpretation. Babies will not always make a sign correctly the first time they sign it, just like they won't speak a word correctly the first time they speak it. Keep signing the word the correct way and your baby will soon grow more accurate.

Be open to suggestion. Sometimes a baby will create a sign for herself. Feel free to continue using it, and applaud her creativity.

Be praising. Act excited when the baby uses a sign correctly, and let your baby know how wonderful you think he is.

Be expressive. Use your face and body in addition to your hands. You can also say the word as you sign it.

Be patient. Babies can take weeks or even months before they make their first sign.

Most importantly, don't think of signing as a skill that has to be mastered. Instead, think of it as what it is intended to be - a bridge of communication before your baby can talk!

Monica Beyer is the mother of two sons and has been signing with her younger son for over 1 year. Visit her website at http://www.signingbaby.com or email her at monica@signingbaby.com