What is the goal? To obtain a certain grade? Just to pass? Try to be realistic with your goal. You should make you study schedule ASAP and stick to it. Eliminate tasks during your study sessions not related to the test or exam you are preparing for.
Study during times when you are motivated and able to focus. Have everything you need in order to studying. (review notes, practice questions, water, snacks) Have something to work towards that brings a sense of accomplishment or reward yourself for a job well done.
getting to work
Stay focused during your study sessions. Be prepared by making a realistic study plan. Know how much time you are going to study, and be in the right head space. If you are struggling with any of that take a break and come back to it. You don't need to start your study session over again just complete the time you committed to.
Speak with your teacher(s) during & after review has been given to answer any questions you have. Make sure you're completely clear about what you need to study for. If you are feeling overwhelmed talk to your teacher. You could also reach out to a parent or another trusted adult for help. Whatever your goal is in regards to achievement be willing to sacrifice and renegotiate other responsibilities you have. Be proactive as possible with this. People that these decisions are impacted by will be more understanding.
Stress management is key when preparing for tests or exams. The more prepared ahead of time you are leading up to the test or exam the better. Having a studying schedule and sticking with it will help in managing the pressure. Be prepared that you may become overwhelmed. Take a break, use mindfulness strategies.