The issue with threads like this is that although there may be some good suggestions that come, many of the replies (including this one), will not really be of help to someone trying to troubleshoot their issues. What would be good is if someone could curate the suggestions and create a document which could be placed somewhere like this to serve as a reference.
A suggestion oh how to determine between two mistakes that can lead to film coming out clear (both of which I have done):
If there are edge markings on the developed film, but no images, was the lens-cap on when you shot the roll?
If there are no edge markings did you process in the order fixer, stop, develop rather than develop, stop, fix?