How can I improve

Hello in one week I'm gonna have my second midterm and I'm feel nervous. I understand a bit the topics and to be honest my teachers are not the best-teaching , the last two exams that I have were awfull but I recognized my mistakes and now I know that I have to be more attentive to details. Any way does any body have any suggestion because I want to learn math from my own as well as practicing the topics that I have on college. Although I'm starting learning the basic by my self like arithmetic and that.