People learn courses differently than others. I go by numbers. I memorize the jump with the number..other people memorize it in lines. Like, single, diagonal, outside line, etc.
The best thing to do as someone said above, don't memorize more than 1 course at a time unless your brain can manage all that. Look at the course as your next to the ring and visualize yourself riding the course. Think to yourself, "What will I have to do from fence #4 to fence #5?" or "I know the outside line is a forward 6 stride line, so I better keep my horse forward through that turn so I can get that 6.."
Visualize the flow of the course, and make a plan. Having a plan always works out in your favor. If all else goes to hellwater in a hogwash, at least you can still stick to your plan so you don't completely fall apart. Plans are easier to stick to than going in blind.
But don't worry, if you go off course you go off course. Everyone does it. It's part of learning. :)
In riding, a horse's energy is like a river- guided by the banks but not stopped by them.