THe only advice I would add to the others, is something I read in my book "Baby Signs". And that is to make sure you incorporate "highly motivating" signs to the signs you teach your baby, instead of only doing the signs you want her to know. So I started with doing about 10 signs total so as not to overwhelm my son. I did half objects my son loved to do, like ball, rock, keys, and the other half were ones I wanted him to be able to communicate like milk, more, eat. He did his first sign at 7 months and now has MANY signs (18 months old) in addition to a few words.
It really helps because his words duck, truck, cracker, and yucky all sound alike when he says them, so if I ask him to show me with his hands, it really helps clarify. "Oh! You want to eat a cracker!" and he gets one. It has taken so much frustration out of our communication. If he gets mad or whines I tell to "tell me nicely" and he immediately signs what he wants or what is troubling him. It's great because he has learned that he gets results when he communicates nicely wiht his hands and words, and not when he hits or whines. If we didn't have signs, I'd have to guess what he wanted when he cries and we would both be frustrated. Plus it's cute! and my extended family knows the basic signs (I look them up in my book or online when I need a new one) and can watch him and know when he's hungry, wants his blanket, hears an airplane etc. The "highly motivating" signs are fun for him, and he uses them constantly and learns them instantly after me showing him one time now that he's older. He loves to tell me about the truck or the airplane we see. And he can tell me if he wants to "jump" on the trampoline or go on a walk. It's fun! The book I have is full of fun activities to do with signs to help make it fun and bonding for both of you.