This is from Itty Bitty Signers / Sign Language Academy. I liked it. :)

Key Points To Remember When Teaching Your Baby Sign Language

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   Though it is never too early or too late to begin signing, the general rule of thumb is to start introducing signs when your baby is approximately six months old. Your baby’s memory retention is not well developed until then and you are less likely to become discouraged and give up if you do not have to wait too long for your baby to begin signing back.
  
•  Is your baby receptive and ready to begin signing? The common indicators are that your baby should be able to sit independently, maintain eye contact or hold a gaze for more than a couple of seconds, and be able to point, wave bye-bye and mimic other similar hand gestures.
  
•  Repetition and consistency are vital to your baby’s ability to recognize that signs have meaning. Babies generally produce their first signs somewhere between the ages of eight and twelve months, with the average being ten months old. Your baby is much more likely to begin signing sooner than later if you sign with her on a regular basis.
  
•  Your baby may watch your hand movements more intently once he makes the connection that these gestures have meaning. While he may still not be able to physically produce signs, you can tell he understands if he reacts excitedly or looks about when you sign to him.
  
•  Your baby will likely start playing with her hands in an attempt to imitate the signs you are doing. Though intentional, these first attempts are usually more experimental movements than actual signs.
  
•  While baby is still figuring things out you can expect your baby’s signing to occur intermittently at first. You may find that he signs one day and not the next for a short period of time. He might sign out of context and use one sign to communicate many different words and ideas.
  
•  Be on the watch for your baby’s sign approximations. Your baby will make signs in a way that is easiest for her and may not produce them properly in the beginning. She may mirror your signs - making hers in reverse (like bird), and use the same gesture for words that are signed similarly like bear and hug.
  
•  Most importantly - No Pressure! Relax, be patient, and have fun signing with your baby. Do not fret if you think your baby is not getting it and don’t make him feel you are disappointed if he does not sign. Remember that signing with your baby should in no way be a chore for either of you.
  

Tips For Signing Success Tips For Signing Success

•  How many signs should you start with? A recommended guideline is to start with maybe two or three signs that have meaning to your baby and add signs as you become more accustomed to signing. However, it is also perfectly fine to use as many signs as you know. You know yourself and your baby best so teach signs at a rate that suits you both.
  
•  Which signs should you start with? Any signs you like! The most common are milk, more and eat because they are easy to learn/remember and, being needs based signs, they are what very young babies fuss about most.
  
•  Make sure you have your baby’s full attention when introducing signs. Make eye contact and sign just below your baby’s line of vision. For very young babies sign close to your face.
  
•  Allow signing to happen naturally, keep it real and use signs in context.
  
•  Help motivate your baby to sign by teaching her signs for objects that seem particularly appealing to her along with any needs based signs. To optimize signing success, teach your baby a combination of needs based or routine signs and motivating signs.
  
•  Speak the words you are signing aloud as you sign them.
  
•  Use signs as part of your daily routine. Once you have chosen your initial signs, use them every time it is appropriate, i.e. if MILK is one of your first words, sign MILK each time you give your baby milk. As you add new words, use them consistently and frequently.
  
•  Model new signs before, during and directly after you show baby the item related to the word you are trying to teach. Make the sign a couple of times each time you use it, using slightly exaggerated movements.
  
•  Use picture books, magazines, songs, nursery rhymes and play objects to introduce signs that your baby does not ordinarily come in contact with or see on regular basis.
  
•  To help teach signs for intangible concepts like hurt/pain, sad, happy, etc. be an actress or actor and use appropriate facial expressions.
  
•  Encourage baby’s attempts at signing by giving him lots of hugs and positive attention. Avoid pressuring baby to sign.
  
•  Enthusiastically acknowledge your baby’s sign approximations while saying and correctly modeling the sign your baby is trying to do.
  
•  Teach family members, caregivers and anyone else close to your baby some of the signs you are using. Encourage them to sign along with you so that your baby will be exposed to signs regardless of whose care she is in.
  
•  Finally....Make Signing Fun...Have a great time with it and remember to enjoy this wondrous time signing with your beautiful baby!