The 3 usual questions #2: how do you guys learn all those lines?

Repetition and hard work. Whether that's a method where you make a recording of your lines and listen to it over and over, or you read your lines over and over, or you write them out longhand, or you get a friend or fellow actor to run lines with you, you've just got to do them again and again.

A few things that are helpful.
1) Figure out the meaning of what you're saying - it's got to make sense to you before you can learn it.
2) Figure out the reason you're saying what you're saying - is it because you're trying to intimidate someone? or trying to flatter them?
3) Figure out what you're responding to - is this thought in response to something someone else said? Is it further clarification for what you just said?
4) Picture the action that goes with the words. Knowing that you say certain words as you fall to your knees, or turn away from a fellow actor can provide the juice that gets the lines memorized.

Other than this it's a lot of drilling and repetition. Definitely not the glamorous part, but also not the hardest. Learning lines is a basic component of every role an actor plays, so the experienced actor knows what methods work for them, and gets this part of the job done.