There are a few basic things that your rat needs you to do for him or her.
Providing a good, stable diet, along with a constant supply of fresh water
Another rattie friend. No matter how much time you spend with your rat, you can't replace the value of having another rat friend in the cage. Keep rats in same-sex groups to avoid unwanted breeding or make sure that your rats have been neutered/spayed.
A nice big, clean cage
Excellent veterinary care
At least one hour play time with you every day (outside his/her cage)