Prior to kidding, or in the actual stages of kidding?
Prior to kidding- easing weight from one back foot to another, nickering to her sides, flicking her ears back, sometimes discharging from the vagina. You may notice if you have another goat next door to her, that the other goat nickers to her side- they are talking to the kids as they can hear them.
Actually kidding- Definitely discharging from the vagina, which also should be quite slack. She should start to have contractions, and push fairly regularly. If the discharge is dark, bloody or smelly, something is wrong so get the vet or a shepherd. Equally, if you have seen her properly pushing with discharge, and she stops- get a vet or shepherd. It means she has given up, and she needs to be kidded. Goats will sometimes give up pushing even when its something simple like a breech birth.
Beth