Masteries
Masteries aren't as crucial to one's performance as runes are, but they're noticeable when you're playing for the first 10 or so minutes. There are 3 trees of mastery, Offense, Defense, and Utility. You generally go down the Offense tree for AD characters, Defense for tanks, and Utility for mana-reliant/AP characters. You unlock 1 point per level, up to a total of 30 points. The most common way of doing masteries is putting 21 points into one tree, say offense, and 9 points into another tree, ending up with 21/0/9