How to improve in math?

I'm in my first year of bachillerato/high school (Spain) and I'm currently studying derivatives (and to be honest, I've been terrible at math since the second year of ESO, although that's because I developed a dislike for the subject back then due to a teacher who made my life miserable just because he didn't like me).

Although I'm improving, I have a math exam on derivatives in two weeks, the end of the term. While passing math isn't essential, I want to improve personally, but I don't know where to start or what to do to improve, such as how to better understand or memorize formulas, how to enjoy it without getting frustrated, and what I should do.