I think that in any situation a good way to sort out the relevent from the irrelevent is to remember to look for that information that helps you reach some sort of conclusion or if not itself an end but a means to an end.For example if you want to take travel to a certain city by route and dont know how to get there a good way to start would be to look at relevent road maps that give you the possible routes to the place you want to go including other places. Naturally your focus would be on figuring out the best rout to the place your interested in travelling and so all the other irrelevent routes are immediately hold no importance and youre well on your way to figuring out to reach your goal.
So i think in my view an easy way to sort out the relevent from the irrelevent is to focus on your topic or the issue at hand and then make sre you realize what exactly the situation implies. It is only when you understand the question or situation properly can you then proceed to look for what is relevent or irrelevent.
I think a lot of times we focus on solving the issue too much but i think if we spent an equal time on understanding the questions put forward or the situation we find ourselves in a lot of the complexity we feel the issue presents would dissapear and thus finding answers would be easy.