What's the best way to remember your lines? Mean what you say.

First thing you do is read it and read it again, and read it again, and read it again, because the most important thing to lay the basis for memory is to really understand the meaning, the deep meaning. Then when you do that, you then go back to the beginning and now that you have a knowledge of the essential core meaning . . .

You ask yourself 'What am I really trying to get from the other person or do to the other person? What behavior can I see in the other person that will make me know I've achieved my goal at this moment?'

But understanding is only half of it . . . the other is something Tony calls active experiencing:

. . . 'active experiencing' is not a theater term; it's what my wife and I coined to describe to psychologists. [Active experiencing] is really meaning what you are saying and meaning it in terms of the other actors -- really looking them in the eyes and trying to affect the change in their eyes by influencing them with whatever you are trying to do at that moment . . .

What's fascinating is that learning lines this way seems to not only improve an actor's memory for specific lines -- it also improves memory in general: when people, non-actors, in their 60s through 90s learned this technique, this approach to remembering dialogue, their ability to memorize anything else also improved (What Studies of Actors and Acting Can Tell Us About Memory and Cognitive Functioning).

P.S.

Prior to meaning what you say, you need to understand what you're saying. William Shatner explains what to do first: