Keep up with the class. Our class gathered over 300 plants, and without constant upkeep of your knowledge you will quickly fall hopelessly behind. It doesn't take much, but it must be often. Organize your collection. There are numerous ways to do this, each with their advantages and disadvantages.
Some people organize their plants by family.
This is good to see common family characteristics, but I found that when studying a group of plants in the same family I tended to simply say. Oh, that's an Aster because the last plant was, too. Another way to organize your collection is by site. This is a quick and dirty way to focus your studying on the plants you suspect will be at the next location. I figured out about halfway through the semester that I really did have to know all the plants we had covered at every location.