One fun technique is silly mnemonics. It requires a bit of creativity, but, for example, take the defining expression for entropy : Entropy (S) = boltzmann's constant (k) times the sum of p*log(p), where each p is the probability of a microstate. If I wanted to memorize this using a mnemonic, I might make up a story about it. Boltzmann is a wizard building a wizard tower, and the wizard tower is made out of logs. He makes these logs out of a huge pile of peas he is standing beside, and also makes from these peas the pea-green paint that he will paint his tower with. The tower is called "the tower of entropy," and it will have a big S on the top. Boltzmann floats the peas past him, and some of them turn into logs and some of them turn into paint, and then he paints each log and adds it to the tower.

So now I'll remember the formula for entropy.