Usually I have researched everything about the doctrines, philosophy, time periods, schisms, terminology and after that I view the religion against the backdrop of its time. Also, if it traces back to another earlier religion, that is worth looking into. If it has produced offshoot religions, they are worthy of investigation as well via comparative study.
Do you look at the followers of the religion and/or do you read what the religion has to say (basics, sacred texts, etc)? Do you have another way to look at a religion than these two? And why is it your preferred method?
IMO, religion is a matter of actual belief and practice, while recognizing that it's something engaged in by a community. It's a matter of communal standards that are arrived at by consensus (either explicitly or implicitly)... sometimes with multiple levels (e.g. a declaration of faith that everyone is "supposed" to follow and a set of unwritten rules that people actually follow).
The actions of individuals - even extreme individuals - are part of the mix, since they're just as much a part of the "consensus" as anyone else, but the critical mass of that consensus may disagree with what they're doing and try to pull them back.
Scriptures can be part of all this, but their role in the religion will be determined by the beliefs and practices of the practitioners about how their scriptures should be used.