I have been raising milk goats for a few years now. I started out with mutt goats and have since upgraded to registered Nubian goats. I'm no expert by any means but I've learned a few ways to help keep my milk goats happy and productive.
General health. If you want your goats to produce they must be healthy. Some of the ways to keep them healthy are just basic good husbandry including:
Provide adequate shelter from cold, sun and rain. Goats do not like to get wet. They think they are made of sugar and will melt. Also, if they have to stand in wet or mud they are prone to foot rot, which is a horrible problem to have. They need a dry and warm (or cool in summer) place to rest and chew their cud.
Provide adequate health care. This means make sure they are wormed regularly and properly. Do your research or ask a vet or other goat expert. Do fecal exams. Make sure they aren't carrying internal parasites. That is one of the most frequent and deadly problems in goat herds. They are chemical wormers and herbal wormers that can be used to keep them free from internal parasites. Sometimes they get external parasites like lice. Make sure you get rid of those too. If you want to go natural, use DE (diatomateous earth) or there are plenty or chemicals to put on the goats to get ride of the lice.
Another aspect of health care is keep their fee trimmed. Goats feet, like all hooved animals grow constantly. They need to be trimmed unless you have plenty of rocky ground for them to roam on. If their hooves get too long they start to curl up or under and cause pain for the goat when walking. If the goat is in pain they will not produce as much milk.
Another aspect is to give them their vaccinations. There are several different vaccines that can be given to goats and you can ask your vet for recommendations. If there are lots of skunks, opossums, or raccoon, then it's a good idea to vaccinate them at the minimum for rabies.
Provide them with adequate food. Goats are browsers not grazers. This means that they prefer the leafy hay. And in my observation of goats, the certainly don't eat everything. In fact they really are quite picky. If they don't like the hay, they just won't eat it. Same goes for the brand of grain! However for our purposes of milk goats here my suggestion is to feed your milking girls the best feed and hay possible. It's a good idea to feed alfalfa hay, or sudan hay or if you have a good source of another type of leafy hay then go for it. The feed you give them should contain plenty of oats. Provide a source of mineral and baking soda free choice is helpful to the goats digestive system. The milking girls are putting out a lot of energy producing that milk. If you don't feed them enough or correctly they will drop weight and production.
These are the basic suggestions for getting your milk goats to produce lots of milk. I'm sure there are more but these will get you started. Use common sense and take the best care possible and you will have happy goats that provide you with lots of excellent milk!