Step 1. Pick the words you want to teach first. I always start with these three (I introduce them at the same time): eat, milk, and more. Here are the signs for these 3 words (these are standard American Sign Language signs)...
Step 2. Whenever you ask your little one if they want to eat, just do the sign! The same goes for "milk" (I use the same sign for both bottle and boob). Use "more" when not only talking about eating/drinking, but playing too! Be sure to say the word, not just sign it.
Step 3. After doing the signs to your baby for a few weeks (I do 2 weeks) take their little hands and mimic the sign for them. You say "Do you want to eat?" doing the sign yourself and then repeat it bringing their little had to their mouth.
Step 4. Be consistent! Encourage family members (big brothers and sisters love doing this!) to help. Teach all the care-givers the signs and ask them to do it too. It seems like it takes my babies about 3 or 4 weeks and then BAM! They totally get it! The first time they do it you're like, "Wait... Did they really do that or was that a fluke?" But then they do it again! Sometimes they do their own variation so be aware of their hand movements. When you see them do it, be sure to verbally acknowledge that you understand them. "Oh! You want MORE?" (still do the sign). It's soooo exciting and fun to have your BABY clearly communicate with you! Yes, people might ask you if your baby is hearing impaired (this happened to us!) but smile and explain what you're doing. Many people are blown away by this, especially when they see your baby do it back! After mastering these words, add on! We did "all done" and "help" next. Try to pick things that they really need. Google the word you want along with ASL and hit "Images" to learn how to do it, or make up your own sign!
Some people think that doing signing with your baby will delay the verbal language development. Nope! The opposite is actually true! Babies who sign have a much higher vocabulary and pick up new words much faster than those who don't sign. Not to mention studies show they have higher IQ's plus a slue of other amazing benefits... (See the links at the bottom of this post.)
I first learned about signing with your baby in some of my psych classes while earning my degree in education. I knew right away that this was something that I wanted to do with my future children. I purchased a program for my first child. Here is the one I used:
http://sign2me.com/index.php?option=com_content&view=article&id=14&Itemid=242
Dr Garcia made it so easy to do!
Here are some links with some of the many benefits of signing with your baby:
http://sign2me.com/index.php?option=com_content&task=view&id=15&Itemid=31
http://theparentsite.com/parenting/signbaby.asp
Happy Signing!!!