So after performing a long piece of Cowboy Poetry at a recent event, a young audience member posed that question to me. I usually have a quick answer for young fans - 'lots of vegetables, lots of sleep, and lots of practice!'
But it's a great question and really there's no easy answer. I use a few techniques - they work for me and maybe they'll work for you.
First off - I'm an auditory learner. I learn better by hearing something - that's what works for me. If you don't know what kind of learner you are - check Google - I'm sure there are no less 115,997 search results for determining your preferred learning style. For me - it's Auditory.
Second - I never, ever, ever try to memorize a "normal" story. That's my style and the first rule of good storytelling is to be true your own style. The only memorizing I do is for my western or cowboy poems. The reason is pretty simple - I spend so much sweat and energy and burn through so many pencils making a piece of poetry just right. I feel like it's got to be performed exactly that way - so...
1) Record it and play it back. My most recent and successful techique is to make a recording of me reading the piece. I record it once or twice - not very good quality most of the time - and then burn the best copy onto a CD. I put it on the CD three times. That way as I'm commuting or hanging around with nothing to do, I can pop in the CD and HEAR myself delivering the poem. After a few listens I begin to tell it along with the recorded version. Finally, after many repeitions of this process, I'll have it down.
2) Perform it aloud to just myself. Generally, I have the basics learned and I use this step to clean up and passages that particularly sticky. Moving between stanzas is usually the hardest part. I don't worry about standing in front of a mirror or anything like that. I just perform it over and over to get it down and get over any last humps.
3) Perform it in front of my wife. She's the best audience - and no, that's not because she always loves my stuff. No, it's because she has an appreciation for what i'm trying to do, where the story is trying to go, and how it plays to audiences of different kinds. Now, you'll have to find you own audience of one to listen - she's taken.
4) Practice, practice, practice. Take individual sections - start in the middle - practice in environments where there are interruptions - run through your piece while shopping or painting or other non-event formats. And don't get discouraged - you'll get there.