The first step before we study is learning to take notes. You could do it with pen and paper or on a laptop (the scientific studies about the effectiveness on each of these methods are diverse and have not yet come up with a decisive conclusion). There are also different ways you can layout your notes. The video below shows a quick overview of the most common layouts.
There are a few things you should be doing no matter how you take your notes.
Go to class! It sounds silly to have to say this but turning up makes it so much easier to learn the concepts. Your teachers are there to teach you and they are pretty good at it.
Take notes. At high school, most teachers will give you summarised notes to copy down. I recommend writing these down verbatim (i.e. as it is on the board). You can use some study techniques at home to reorganised this information in different ways. You could also jot down some notes when the teacher is explaining things if you think this will help you remember later on. Remember that if you find it too distracting, it is better to prioritise listening to the teacher.
Be prepared. Bring all the equipment you will need for class. Be it a periodic table, a calculator or your copy of the novel. Read ahead in your textbook or watch the video for the next lesson so that you go into class with some idea of what the lesson will be about.
Catch up. If you are away for some reason it is your responsibility to catch up on any learning you missed. Ask your teacher for any handouts or links they used and copy the notes from your classmate.
Finish your work. If you run out of time in class, your first thing to do in your study time is to complete any unfinished questions or activities. Check your answers against your classmates or ask them for help. This way they learn it better by teaching you and you learn how to do it. Of course, your teacher will be happy to help you too. Just make sure you ask them at a time when they are not busy teaching or prepping lessons!
Ask questions. If you are confused, ask a question. It will help you learn and there are probably four other people in that room with the same question. Use your bravery and speak up! You can also ask related questions to clarify your understanding.