Here’s a video I made a while back about learning, which is a passion for me. (Now, I’m more skilled in study technique than in making videos, so please excuse the video quality, and send me constructive feedback!)
I talk about the value of self-testing, of increasing the challenge to the right level, and weird mnemonic visualisations for language learning. Particular techniques mentioned include spaced repetition (e.g. Anki, but I first did it in 1995 with vocab lists on strips of paper) and interleaving (incorporating older material with your newer study content in order to strengthen those memories).
The main thing to remember is this: Keep your brain engaged and exercise your memories by testing them, and you’ll get better results.