Work hard and do the best you can. Don't plan on extra credit to save you in the end. You should strive for the good grades in the first place!
The most important thing is to pay attention in class. All of the teachers give you exactly what you need to succeed. If you are not paying attention in class then you have no one to blame but yourself. School comes first, socializing can happen on the playground and not in the classroom.
Remember! Your education is what YOU make of it!