Some simple rules that might help. And yes they make great pets, if cared for properly they can easily reach 4 years of age.
1. Avoid petstore rats. Find a rat breeder ( the kind for pets not food! ), it will be much healthier and better socialised, ie making a better pet fullstop.
2. Get two, either a pair of females or a pair of males. They need company of their own kind. Males will get along if raised from a young age.
3. Females are more active and playful, boys are much more laidback and enjoy cuddles. Females are more prone to tumors however. Tumors are very common in adult rodents, usually non cancerous so does not cause a problem until it gets too large. You can either opt for surgery to remove them, but often will grow another very quickly, or when you feel their quality of life is reduced simply have them put to sleep.
Avoid fishtanks for housing them ( bad air circulation ), also cages that have wire floors. Best bet is something like a reptile enclosure that has solid floors, and a few different levels, with a door at the front made of mesh. Lay down fabric or newspaper as substrate, with a large box somewhere with shredded paper they can play in.
You can toilet train them to use a certain area so if you do this its much easier on cleaning.
Anything else just google, google is your best friend for this kind of info, there is tonnes of websites about rat care!
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http://www.dapper.com.au/ (awesome site)
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http://ratguide.com/care/
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http://www.petratscanada.com/ratcare.htm
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http://www.ratz.co.uk/