No matter what your background with using sign language, it doesn’t take much to get started. As you can imagine, babies can only handle a very small vocabulary to begin with, so you will have plenty of time to build your own vocabulary to teach your baby along the way. My personal choice is to use American Sign Language, a visual means of communication that uses hand movements, facial expressions and body placement to express language visually.
As you explore ASL, if you have not already, you will notice that many of the signs are difficult for little fingers with limited dexterity to maneuver. It is the decision of the parent if you want to use an alternate version of some of the signs, or consistently model the actual sign from ASL. Little fingers may come up with their own version regardless, so part of the parent’s job is acting as an interpreter of your baby’s gestures and signs. As they mature and their hand control improves, so will their ability to form signs correctly.