I began Starting Strength a week ago, and just finished my 4th workout before class and the effect was significant enough that I will now continue working out before class for the foreseeable future.

Basically, you'll feel a post-workout buzz, you'll be more focused, and it will take significantly longer for the tedium of the class to eventually break your attention.

It's not much as advice but it's one tiny little extra motivator to lift: it will make your classes suck that much less.