Utilizing as many senses as possible is an effective memorization technique. Actors write out their lines (touch), say them out loud (hearing) and read them off the page (sight).
Remembering meaningless data is extremely difficult. By focusing on the meaning of the words, actors can memorize their lines in the context of the play as a whole.
Large chunks of text can be broken into smaller sections, called "beats," to make memorizing easier. Each beat may have a specific theme: for example, the actor may be manipulative in one beat, and pleading in the next.
By thinking of the lines as relating to himself in some way, the actor can memorize much faster.
Moving around, using gestures or going over the blocking of the play while saying her lines helps the actor remember the text.
A cue is a word or action that comes right before an actor's line and helps him remember it. For example, the cue for Hamlet's "To be, or not to be" speech is the exit of the king.