Begin by breaking your speech into main points and memorizing just what the main ideas are. Write them on a notecard and rehearse saying the main points back to yourself. This will be helpful if you get stuck or forget the precise wording you can continue on with the main ideas of your speech.
Then practice your speech one small part at a time. Rehearse reading that part and then saying it back to yourself without looking at the words. The most important thing you can do for yourself is give yourself ample time and practice to master your speech. Do not wait until the last minute to go over it. If you break it into main ideas and then practice each section thoroughly, you can successfully memorize your speech in time for the presentation.
To start memorizing your speech, you can start small. Memorize a few sentences at a time until you start to get the hang of it. Then, you can try to memorize bigger parts of your speech.
A useful tip is to have key words in every couple of sentences because those key words can help trigger you to remember other parts near the key word. You can use flash cards to memorize your speech easier and test yourself by not looking at the writing. Another way to memorize is to write down your speech on another piece of paper while not looking at the original. Practicing in front of a small group of friends can help you be prepared.
On the final day before your presentation, practice saying your entire speech with no help. If you say it out loud perfectly, then you should be ready for the presentation. Remember that this process will take time so don't procrastinate.
What I like to do is practice in front of the mirror, so that way, I can be comfortable with actually delivering the speech and I can practice my tone and different inflections in my voice. This constant repetition helps me remember my speech as well.
However, before I give a presentation, after I write it, I plot it out on a map/graph. I have a graph of 4X4 square. In each square, I write out the main idea. For example, in the first square I write out my intro. Then I draw an arrow to my second square, which has my thesis. Then I draw an arrow to the next square with the claim of my first supporting paragraph. The arrows can go in whatever order they want, but the information is organized into however many squares you want. This way, by dividing your speech up, it forces you to think about your speech and how it works together. Then, in case if I forget something when I'm delivering the presentation, I can quickly glance down at my chart, get the "key word" which will trigger everything related to it.