I design my sermon through mind mapping and take the mind map with me to the pulpit. Sometimes I look at it if I have a long quote. But you will find that it is much easier to memorize your sermon easier using a mind map. Perhaps "memorize" is not a good word, "visualize" is what you are actually doing. This book and the diagrams are in black and white, but before I preach the sermon, I take out my colored markers and go to town. Different colors are given to different points. This will also help with memory. Sometimes I feel like a little kid with my crayons. No one said preparing a sermon can't be fun.