1. Get two rats at the very least, loner rats can have many health problems.
2. Don't feed them anything from the petstores, it's cheaper and healthier to make your own mix(google Suebee's Diet).
3. The cage should have two square feet for each rat.
4. Well-bred and hand raised rats love affection and play, take them out and play with them as much as you can.
5. Teach them their names and teach them to come when called for. This can usually be done by holding them and constantly saying their name while scritching and whatnot, then to teach them to come associate a sound and the one-word command(like shaking the yoggie box/bag and saying "(name), Come!")
6. Have a GOOD rat vet in mind, one who has experience and knowledge, not just one who is willing to handle rats.
Good luck and have fun with your rats!