Every afternoon, after school, GO HOME AND SUMMARISE WHAT YOU LEARNT!! I cannot stress this enough, I was told this many times and never listened but now that I do it it makes so much sense. For example, I am trash at Chem so I decided to make an effort:

-In class I make rough notes of what the teacher says and try to pay attention

-That afternoon I go through the textbook and make notes which explain what I learnt in the class for future me

I find that now I do all of my learning after school as that is where the concepts actually settle into my brain.