oh ! i just had my chemistry half yearlies today.
what really helped me was doing practice questions and review sets in my textbook.
its really good because everytime there's a question in the review sets i don't understand i'm forced to look in my textbook for the answer.
trust me practice questions really help
even if you find the questions too hard. force yourself to answer them and don't give up!
also revise you're notes from class and past experiments conducted.
i prefer revising by making mind maps cause when i walk into the exam room i remember the image of my mind map
but everyone's different so it may be the same thing or something else for you
good luck