Usually, it happens that whatever we learn, we forget it after sometimes. There are some tricks to fit a thing in our mind forever:
1. Try to connect it with your surroundings. Always remember any fact with an example.
2. For remembering a formula, write it on a paper and stick it on a place where you always happen to see it. You don't need to remember it, you just have to look it.
3. Revise the things. First revision should be after 3-4 days. 2nd revision after 10 days and third revision after 28-30 days.
4. Practice the things as often as you can. If you want to be best at something, you will have to spend more time doing that thing.
5. Read a book of your interest. It increases your thinking and imagining power.