A few years back as a birthday present to myself a buddy of mine and i went to go get film developed. With me I had brought 20 odd rolls of undeveloped film taken on a hardly tattered, untested T70 SLR that was bought secondhand as a starter camera, with various brands and exposures of film. Of all the rolls of film, not a one was salvageable . The negatives were all blank/black. Fast-forward: here I am today, with another untested camera which I’ve been shooting a great deal of undeveloped film with and would like to know of ANY tips as to taking the proper precautions to avoiding blank negatives in the future. Also, what might be my fault in 20+ blank rolls of film.
As a first obvious point, don't shoot 20 rolls of film when you are just testing a camera – shoot one and have it developed. One roll is enough to test a camera – then you can begin to use it for actual picture making.
With respect, what is your expertise in photography? Can we assume that you were using sensible exposure settings? That is, aperture, shutter speed. Did the meter readings from the camera correspond somewhat with the "Sunny 16" rule?
I think to answer your question, you need to maybe provide more information... How did you store all those rolls of film? Did you do anything with them which you yourself think could have caused any issues?
In the meantime, there are a few questions on the site already that have good information for you: