I do not take breeding lightly and 99 times out of 100 if you are breeding I will tell you that you should not be breeding. However, if you are truly interested in breeding there are some strict guidelines that I feel a person must follow. I was going to type out my long listing of what my breeding beliefs are however, that has already been done and rather than reinvent the wheel I am going to just link you to a breeder's web site.
Bao Varakhii Rattery is based out of Michigan. It is one of the oldest, largest, and most reputable ratteries in the rat world. He has written a great article called "Should I Breed my Rats?" Word for word this article expresses everything I want to say. Please read this article over and if you can not follow this article to the letter then you should not be breeding your rats.