It is very much depending on the topic. What usually works well for me with technical stuff is just doing the thing. Write a little program, play with it, crash

It is very much depending on the topic. What usually works well for me with technical stuff is just doing the thing. Write a little program, play with it, crash it and repeat. For supposedly superficial knowledge and mathematics etc. the good old presentation is very helpful for me. At the moment you try to condense and present it, everything changes. What was obvious or clear becomes difficult to tell and this are the bridges that will help a lot later. To quote one of my professors in loose translation. "I don't know much about that topic yet, maybe I should make a lecture for it." Retention by creating course material is quite powerful and can be very deep.