It took a while before Gab communicated with us thru baby sign language. It took about 2 months for us to notice that he is signing to us to communicate what he wants. It just started with these five simple baby signs: Milk, Eat, More, Dad and Mom.
These five signs will be most used when the baby is growing up. You would probably be using them everyday which makes it relevant. I suggest starting with these five signs first. Avoid adding new signs until the baby knows how to sign back at least 3 of them.
At the same time, be patient. We started showing these signs to Gab at 6 months but he was able to do the sign on his own at 8 months. Repetition and consistency is the key for learning.
Gab and the baby sign for Mom. Not a perfect execution but he gets the point. 
Illustrations below were taken from http://www.babysignlanguage.com
Baby Sign – Milk
The baby sign for milk is done by squeezing your hands like you are squeezing milk from a cow’s udder.
Show the sign when giving milk to the baby. You can show the milk bottle and sign at the same time. Avoid showing the sign when the baby is already hungry and crying. The baby will not understand you at all. Better yet, show the sign once he has calmed down and already drinking his milk.
Baby Sign – Eat or Food
The baby sign for Eat and Food is the same. It’s the same way adults would sign to say eat. This is done by letting the tip of fingers touch each other and tap your fingers to the tip of your mouth.
Just like Milk, show this sign when the baby is about to eat. I also suggest showing this sign every time you are about to put food into his mouth or when the baby is chewing his food.
Gab signs for Eat. He’s 11 months old in this photo.
Baby Sign – More
The baby sign for More is done by making an “flat” O-sign with both hands and tapping both hands in front of you.
Show the more sign when you are about the give milk or food to the baby. You can also show the more baby sign when giving out toys one by one. This may be taught a lot later than the the sign for milk and food.
Baby Sign – Dad
The sign for Dad is done with an open palm and tapping your forehead with the thumb.
I think it is more effective if it is Daddy who is showing the sign while saying “daddy”. For strange reasons, Gab learned to say and sign Dad first before saying and signing Mom. But his first attempts were not accurate. His thumb would touch a little above his ears rather than on this forehead. But we keep on praising him for that effort and continue showing him the correct way of doing it. He finally does it well now and even says the word “Dad” while making the sign.
Baby Sign – Mom
The baby sign for Mom is similar to the of Dad except that you tap your chin with the thumb instead of the forehead.
To teach this sign, Quennie use the Mom sign when she is breastfeeding to Gab. Gab learned this sign a little later and sometimes confuses it with the sign for eat like the photo above. I have a feeling he thinks of his Mom as Food. Hehehe…
Teaching Baby Sign Language is easy and rewarding. It takes a while but just be patient and consistent. Soon, you and your baby will be talking to each other thru your hands. It’s a great experience.
Check out books and DVDs on Baby Sign Language at Amazon.com.