Attempt to connect the theory you read with events, songs or people. This makes it easier to remember them. I call this “memory links”. If you link new knowledge to something you already know, you will remember it better.
Some like to use associations where they move through a house. For each room in the house, a word you want to remember is linked to an object that starts with the same letter as the word.
One example of this is the decimals of the number π=3.14159265359…
The house had 1 hallway with 4 pairs of shoes, 1 hat and 5 jackets. The floor had 92 tiles with 65 dots. I moved towards the office which was behind the 3rd door. Inside hung 5 diplomas and 9 medallions on the wall.
Others remember things by making them rhyme, make a rule or make a mnemonic. An example of this is how you multiply two parentheses with FOIL: First, Outer, Inner, Last:
First: a and c are the first symbol in each parenthesis.
Outer: a and d are the outer symbols because they are at the very beginning and the very end of the expression.
Inner: b and c are the inner symbols because they are in the middle of the expression.
Last: b and d are the last symbol in each parenthesis.