...in going over and over every site I could find the main things are: groom it; if the mother will groom it let her do so occasionally, let it snuggle as long as the kittens aren't pushing it away. Keep both ends clean. Feed roughly 8ccs of formula per oz. of weight per day. A three week old kitten should weight about 10 oz. Weigh the kitten daily to make sure its weight is increasing steadily. Keep it warm. Give it physical contact frequently; if you can't hold it, wrap a hot water bottle or 2-liter full of hot water and tightly closed in a blanket or fur for the kitten to nuzzle; alternately, a soft heating pad beside/under the kitten's bedding. Keep the eyes clean. Keep the ears clean. Damp, warm cloth, small strokes all over the body. If the kitten doesn't want to nurse from a dropper/bottle/whatever, rub its tummy, set it on its tummy and rub its forehead, groom it, double-check temperature of formula. A bit above room temperature, WARM but not HOT, if the kitten won't take it try lowering or raising the temperature a bit.

Yes, I've been reading a LOT.