A goats need to be wormed depends on its geographic location, feed lot, number of goats around and its stressed condition.
If fed on a dry lot the need for worming goes down. If on a wet lot (grass) the need for worming goes up. If your location is very wet or local breeders are experiencing worm problems in their cattle horses or goats chances are you are as well.
To check a goat for worms, look at their eye lids and gums. A healthy goats will look pink, a wormy goat will have pale pink to white/gray
To know what kinds of worms you are dealing with you can take a stool sample to the vet. Even a dog and cat vet can run a stool sample and let you know what kinds of worms you are dealing with and if the goat/s have worms at all.
Loose clumpy to runny stools can be an indication of a worm overload. All goats will have some degree of worms, but when the goat gets stressed they cant fight them off as easily and then are susceptible to getting an overload. Anemia can result. Treating an anemic goat isnt always easy. Having some kind of iron injection or iron supplement is good to have on hand.
Worms I recommend (but seek someone in your area who is familiar with what works and doesnt work for your geographic location because in some areas worms have become resistant to certain wormers a vet may also be able to recommend a wormer for you)
Safeguard works for tape worms, use it 3 days in a row
Ivermectin safe even for pregnant does
Verbazon do not give during first 3 months of pregnancy.
Cydectin - not personally familiar with this wormer, hear it is strong but effective
Decomax I hear this is a good wormer, and safe for kids as well, no personal use of the product to share.
If using a horse wormer paste it is best to triple the goats weight and then dial the dosage, especially with safeguard.
Worming every 3 or so months is a good average for maintenance worming.