Patience. When we had kittens born on our property, they were friendly to us but not the mother. By the time we got back from vacation, the window of opportunity was closed for really taming them. They finally trusted us enough to come in the house, eat the food, lounge around...BUT, they never got used to staying inside. They wanted out all the time and you couldn't close the door fast enough to keep them in. We also discovered that along with using the litter (a good thing) they also used my potted plants for a bathroom.