One of my all-time biggest mistakes that I made when taking science classes was that I took the first 2 weeks of school to take my time and get comfortable with the class–but you had to know how my brain worked. When I say that I got comfortable, I mean that I got in as many “welcome back” parties and video game hours before the first test. The teacher started teaching in the 4th chapter so I skipped the first 3 as well, failing to ask WHY they skipped them. Most teachers are assuming that you will read over previous chapters to understand the current one, or that you have had courses that have adequately prepared you for theirs.
The first two weeks of class can be seen as resembling the first 5 yards that a wide receiver in football is running. Jerry Rice–one of the greatest wide receivers to ever play the position–once said that what you do within the first 5 yards that you are running will determine whether or not you will actually catch the ball. The same with most science courses. The first two weeks of concepts will determine whether or not you will catch the keys of understanding later in the semester. Take the time at the first 2 weeks to question your instructor over those basics. Find out which concepts will be necessary for understanding things later and ask them to be specific. If your teacher is as prepared as they claim to be, then they will give you oodles of example as to why you have to know that entire list of terms. It also helps to bring more clarity and understanding as what is important now versus what is important later.