If someone were to tell you everything there is to know about strumming, then firstly they wouldn't be able to tell you everything because I don't think anyone can know everything about anything.. there is always something new to learn. And secondly, it would fill up an entire book. It can't be done in a simple forum post reply. People can give you pointers and common rules that they follow but really it's a matter of seeing how other people do it and copying them.. then after a while you learn your own way to strum. There's no right or wrong way; there are certainly ways to maximise endurance and ways to strum certain styles that are unique to each style.. but there are no hard and fast rules.

You should look for things like "how to hold your pick" and "correct posture" as well as look for rhythm techniques that you are interested in. There's little point learning how to strum (play rhythm) the technique of country/western music if you have no interest in it.. to a certain degree of course. You can always learn something from anything you practise of course. What you are asking is too broad of a topic to sum up in a single or even multiple post response. The reason you keep finding new methods on different sites, is because everyone has a certain way of doing things.