Do you remember all the quotes you heard when you were freshmen, sophomore or junior? Those quotes when they said "it only gets easier as you get older" I don't really think those were true. It gets harder as you get older, and the classes that you need to take are a challenge, but the classes aren't impossible.
As your senior comes closer and closer every year, you should start to think about what colleges you want to apply to. It's something that takes a lot of thinking but you will know your top colleges that you want to apply to. A good key point to keep in mind if you're still young is to document all the extracurricular activities that you do during school, after, or even before. That way when your senior year is here, you have something to look back at and have a reference to any activities, sports, clubs, or volunteer service that you have done. a good way to keep track of it is starting it on a google document, then write the date of the activity, the name, and where it took place. Then when you start your college applications, you can just glance over the document to see what you have done over the past couple of years.
As supposed to your classes, a good key point to keep in mind that although the classes may seem impossible, they truly aren't, all it is is just a challenge. The only way you can pass that class is through doing your work and studying for an upcoming test. Pace yourself as well, with all your classes. If you have homework one night, just finish it up. Instead of spending that wasted hour looking through people's snapchat stories, take that time to incorporate it into your homework. It's no hassle and your grade will be at higher percentage, so why wait until the end when the quarter is almost over?