I'd say fairly easily for me, of course depending on the game. Last few bigger games I've picked up I've been able to read through the rules once through close to when getting it, then skipping through somewhere in the week before I'm actually going to play it with others. Then I'll just be the one frantically going through the rules while playing checking edge cases. I'm weird like a lot of us here and enjoy rules systems and seeing how different mechanics fit together, so it comes fairly naturally to me.