When I first started playing LoL I read quite a few guides on Mobafire, and made my mastery pages based on those. I managed to make up to twenty (the current max) mastery pages, and now I can't make anymore. So clearly I need to start making my mastery pages for more generalized use (jungle/tank/etc), so how should I begin to do that, and how should I categorize?
Best Answer
There is no definitive answer to this question, and I can't make up a special answer for you either, since we know very little about the way you play.
All I can do is give you a few pointers:
Mobafire is a poor reference when it comes to champion builds. The most trustworthy source at the moment is ProBuilds.net (a website which automatically saves masteries, runes, items and spell order data used by pro players in their most recent public games). And even so, you shouldn't trust them blindly. An average mastery page you made yourself is very likely to be better for you than a pro player's one you don't understand. Think for yourself!
If you can't figure out what generic mastery pages should look like, this is an okay start. But you must understand the reasoning behind them, because you will eventually have to optimize them according to your playing style and preferences.
Players who are specialized in a role (top, mid, jungler...) are likely to spend 10+ mastery pages on this specific role, so they will always have an optimized mastery page ready for every situation.
Feel free to leave a comment if anything remains obscure to you, and I will edit this answer.