I'm in Bronze 4, so I try to keep my approach to mastery pages and rune pages as simple as possible. For the five or six champions I play more often I just copy the masteries from a guide on that champion that has good reputation in the community. The problem comes with the other champions. There are too many to have one mastery page and one runes page for each one. Currently my approach is to use generic pages for those champions, i. e., pages designed to be suitable to be used with several champions.
In the case of rune pages I just use two generic pages: a page called Attack Damage for champions who deal mainly AD and another called Ability Power for champions who deal mainly AP. I guess those pages fit most of the champions I play. The problem is that the web page from which I copied those rune pages disappeared months ago, so there's no way of asking questions about them or find out if they are still valid.
For mastery pages I use the pages recommended in this article by Team Dignitas: http://team-dignitas.net/articles/blogs/League-of-Legends/8300/season-6-standard-mastery-pages. That article is nice, but it looks like it's written for people with more knowledge of the game. It doesn't even tell you wich page fits each specific champion, you have to figure it out on your own. For instance, currently I'm learning the basics of Riven top and I don't really know which of the two pages they suggest for tops works with her.
So, where do I get a reliable and small set of generic pages that I can use when I want to try new champions?