My method.
Did this for about 3-4 days.
Learn the first 4 and after that add another 4 etc.
NDB -. -.. -...
AWJ .- .-- .---
You should try grouping the morse codes as above. I use this as a fallback in case I can't remember what the letter J was. I think in my head [a] was dot dahh and then w was dot dah dah so J must be dot dah dah.
For other letters I use the reverse/opposite method. If X is -..- then P is .--.
IF A is dot dah then N is dah dot.
After some time I started to make it a bit more FUN by insulting my mates in morse on paper. I'd write down what bunch of 'unts they are etc.
This doesn't mean I didn't have to listen to morse on tape though. I had to practice on RANT to see if I could remember each letter. The though bit was actually when I heard 4 letters in one go that I couldn't keep up. After a bit of practice I managed.
--. --- --- -.. .-.. ..- -.-. -.- -- .- - .