A good mnemonic is akin to a trump card: it can help you can learn a fact so that you remember it for a long time, even though you have only learned it once. Unfortunately, it can be difficult to think of a good mnemonic. Happily, this skill can be learnt. If you systematically think of a mnemonic for every word that you get wrong, then after a while you will be able to produce them just like that!