We used to go to Tiny Talk classes and they did new signs every week for a 10 week term then repeated. We did basics like, eat, milk, all done, more, bath etc and then subject specific ones like animals, at the park, clothes etc. Our teacher would add in extra signs for the families that had been going for a while. The used the signs with objects to hold and as part of singing nursery rhymes.
We started DS at 4 months and he actually signed milk at 5.5 months and started signing things like "more" and "all done" around 10 months. DD started at 3 weeks old but we didn't do it as consistently with her. We did love the classes though and made some good friends!
Laura