There are a few signs that I always recommend that people start with when beginning to teach baby sign language or American Sign Language to their babies and toddlers.

But, ultimately, it depends on you, your baby and your situation.

I would suggest you start by examining your daily routine and lifestyle.  What are the main components of your baby's life?  What are the important things in your baby's life?  Those items should be the first signs you teach your baby.  There are a couple of reasons for this:

1. If the item is something that is done everyday (or multiple times per day) then you will have a lot of opportunities to show this sign to your baby.
2. If you show the sign multiple times per day to your baby, there is a higher chance your baby will learn the sign quickly.
3. Once your baby makes his or her first sign (and you recognize it), more will follow quickly because your baby will realize that he or she can now communicate with you without crying.
4. Items that are used for necessity are usually learned first, because your baby knows that he or she needs the item and will try very hard to communicate it to you.  You are simply showing your baby how to communicate.

The first signs that you teach your baby will also depend on the age of your baby.  If you baby is 6 months or younger, the most important items in your baby's life will be you and food.  If your baby is about 1 year old, these things are also important, however, other things may also be important, such as a favorite toy, a brother or sister, a favorite book, a favorite food.

Whatever signs you choose to begin with, just bake sure you have ample opportunity to show the sign to your baby.  Your baby will quickly recognize that the sign means the item and voila - instant communication!