The best way to memorize a speech is to have it written down and practice reading it first, before you try to rehearse from memory. As you read several times, practing your speech presentation, you will automatically begin to learn the words. Then, break the speech into small parts and memorize each part, then read the rest. Continue until the whole speech is memorized.
If you have written the speech, it will be much easier to memorize. Read the speech over and over until you memorize the speech. You will memorize easily if you understand the context. Think about the story when you are reciting the speech. Practice as much as you can, read as much as you can. The best way to memorize is to repeat.
To me, the best way to do this is to break it up into pieces and then work on each piece separately.
If you go to try to memorize the whole thing at once, it can seem pretty intimidating. But if you break it into smaller pieces, then each piece doesn't seem so hard to memorize.
Other than that, it's just repeat, repeat, repeat...
I used to be in plays. Shakespeare plays have especially long monologues and memorizing them can be a pain. What helped me memorize was to mark up the text and go at it piece by piece. By breaking up the text into smaller pieces, it made it easier to memorize.
Read it over and over again and practice it over and over again to make sure you have it memorized. Practice with friends and family and remember the main details you need to have memorized for the speech
I hate giving speeches. If you were the one who wrote the speech and have trouble memorizing it, then understand that you will have problems memorizing it. Of course, when giving the speech you won't be able to give it out word for word. So my suggestion is that you write down the major points to the speech and practice saying it naturally out loud and cross out the major points you've come across.
To memorize things I type them over and over again on a computer or I write them repeatedly.