Remember that fact. I knew the play, the story, and the situations surrounding the scenes and the sequence of the scenes, very well. I knew what came next in the play, in a large general sense. This is very important. The actors approach or system to accomplishing this task of memorization is as varied as their are individuals.
Some actors have a naturally easier time then others.
Sometimes one scene or show is tougher to get learned then others, even by those who usually find it easy. Keep doing it. Get a system developed by trial and error. It is the only way. Again, what works for you works.