Try to picture the plant in your mind when you see the card, not just the twig you taped down. Another way to combat this is to look at your cards upside down, and even better is to use classmates' cards as often as you can. In our class, it wouldn't kill us to flip a letter or two in the scientific name, but points were taken off. I am a great speller, but the binomial names don't always spell easily. Try writing down the names of the plants as you study them.
Mnemonics come is various shapes and forms.
Whatever you need to associate the binomial, common, and family names, go with it.