Survival and success do wonders. As does easy access. And mentoring helps a lot.
We run our own ruleset...have for decades...but all the rules are on the wiki (more on that afterwards). And rules mastery and those who read the rules are always rewarded with success. In a good game system this is easy. When survival rate and character growth go hand in hand with Rules Mastery, then people start to notice. One of our guys started to take advantage of some of the advanced rules for spell casting and spell recovery; his caster soon outpointed the others (he became the Mage mentor later, more on that). Another one started to notice the advanced rules for shield use, and his character was one of 2 talk types who survived for over 2 years (that particular group is going strong on year 10 of the campaign). When Rules Mastery equates to character growth and character survival...players take note.
We have all our rules on a wiki. And the wiki has a damn search function. And we have full laptop/ipad compliance in our groups. So every rule is right there. Mages are supposed to have their spell effects and notes up on the screen when casting; and will suffer an initiative penalty if they do not. Make it this easy for the rules to be at everyone's fingertips, and they have no excuse. This way, everyone has the rulebook all the time.
But since it a coimplicated game, as many RPGs are, we started having players with Rules Mastery in an area become mentors to other players. The guy I mentioned above with the spell rules mastery? All the otehr casters sit near him. The tanks all sit near the guy with shield use (and other combat rules) mastery. Mentoring is a very powerful way to create rules mastery, as there is a social expectation between both the new and older player. And the GM is not the only one involved in the use of the rules. Mentoring is one area that we have really sped up our game and one that alows us to use the more advanced rules that would otherwise slow down a game.