Flash cards might remind you of learning multiplication tables when you were in grade school, and may seem incredibly dorky because of that. However, they're an excellent way to learn basic skills, and an excellent way to learn basic strategy.
Flash cards can be used for any and every playing situation. Some people use them for learning every aspect of basic strategy. Others limit them to player options or drilling on less common moves or borderline hands. You can buy ready-made flash cards, but they're very easy to make yourself, so why not save your money for gaming instead?
All you need is some lightweight cardboard or poster board. Office supply stores usually carry these. So do hobby stores and some drug stores. A deck of index cards works fine. Use something that can stand up to some abuse, as you should use your flash cards regularly. Write down each hand on one side of a card (include both the dealer's up card and the cards in your hand). On the back of each card, write down the correct play for that hand. Then run through your cards, reciting the correct basic strategy for each hand.
Putting every possible hand on flash cards will result in more than 300 cards. If you don't want to make that many, simply write in a possible hand on the front of each card (not including the dealer's up card), and write the basic strategy for it on the reverse. As an example:
On the front of the card: 10-4
On the back of the card: Stand on 2 through 6, hit on 7 through ace.
Another option would be to just make cards for the plays that cause you the most problems. Flash cards are a great portable training aid. Make them small enough, and you can slip them into your pocket or wallet for an impromptu drill session when you're waiting in line at the bank, or at the drive-up window at a fast-food joint.