Plan ahead, use a schedule, get good sleep and balance. You are only 16-17 once, have some fun too. Plan ahead and schedule means to sit down and plan your semester out for large projects and exams. Look ahead several weeks for planning of tests and papers due. Look 1-2 weeks ahead to plan for the closest items. When studying stay off social media.
Spend 90% of your time doing what you have to do and 10% doing what you want to do. Dump the girlfriend/boyfriend. Its a waist of time and drama that impacts whats important. Close out ALL social media accounts. Do these three things and you'll have all the time you need to focus and reach your potential.
Buying a planner is the best thing you could do. Write down important dates such as SAT/ACT tests, when different applications open/their deadlines, etc. Write down ALL homework assignments(grades are crucial so you don't want to be that one person who forgot a simple assignment and received a bad grade) and write down any important dates for extracurriulars (club meetings, fundraisers, sports events etc) Basically WRITE DOWN EVERYTHING you need to get done and plan it out so you have adequate time to do it all.
I also like to write dates/assignments in different colors. Color coding everything makes it easier for me to see my schedule as a whole. (For Example, all Bio assignments in green, English in orange, math in blue, important deadlines in red, etc)
Communication really helps facilitate EVERYTHING. For example, I recently became president of a volunteer service club and I'm not always able to attend my tennis practices right after school. I talked to my coach and we worked it out so that if I absolutely cannot make practice, either he could stay later and we could practice one on one, or I could attend a JV practice which is usually later in the evening. Same with employers, I try to give them my schedule a month in advance and that just makes it easier for them to put me into their schedule.
Also, personally social media is very important as long as you know how to utilize it. I keep in touch with the 70 members of my club through various social media platforms because having an announcement in the static-filled daily bulletin doesn't cut it. My advice is that you should unfollow the unnecessary meme accounts and follow asb/club/school sport accounts because they usually post important deadlines or any changes in their schedule.
I would highly recommend the book by Cal Newport: "How To Become a Straight-A Student:
The Unconventional Strategies Real College Students Use to Score High While Studying Less"
It will help you with time management and how to be more efficient.
And despite what one might think, everything is not important. Rank them... often related to how close the due date is, but not necessarily.... polish my shoes can generally fall off the list in many cases.
I think you ask a great question and on this forum I am sure you have gotten and will continue to get sound advice and suggestions on how to manage your time. There are plenty of self-help books like those mentioned above, but it takes time to read, implement the strategy and develop the habits.
The short answer is only you can find the best way for you to best manage your time. There is no one answer that fits everyone because we are all different. There are only 24 hours in a day so overloading yourself past a limit with reasonable sleep is not wise.
I will give you four different examples from one family: me and my three boys (the oldest is a second year Cadet at USAFA, the middle is a high school junior and the youngest is a high school freshman).
I liked to stay busy. My day was fairly structured in that I went to school, did what work I could for the evening during free time and socialized, then had sports practice after school and did home work in the evening. I usually had time for at least 5 to 6 hours of sleep which was plenty. However, I grew up in a different time (fewer games and distractions), in a small town (not much to do) and in a small school (there were 35 in my class).
My oldest set a track in junior high aiming to get an appointment to USAFA or USNA. He did this on his own. He really was forced to manage his time as he was involved in school activities, sports, church, CAP, etc. while taking a very strenuous course load in school. He loved learning but also loved computer games. He required less sleep than me and generally operated on about 5 hours a night. This is something that served him well at USAFA. He was not social so he didn't require social time on his calendar (would have driven me crazy but it suited him). He managed time by prioritizing needs to meet his goals. He graduated in a class of about a 1,000.
My middle child is very social. He loves video games. School is not near the priority to him that it is to my other two boys. He also plays sports, but struggles to find time to get school work done, practice sports, work a part-time job and socialize. He recently quit the part-time job during sports season to give him more time to focus on school and sports. He decided he wanted to keep his social life more than earn money (we will see how this works out when he has no money for his social life). He also doesn't sleep more than 5 to 6 hours a night. He doesn't make good use of his free time in school.
My youngest is the best time manager of the group. He is very involved in school, extra-curricular activities and likes gaming. He has a small social group, but they are close and do a lot together. He works on school work during free time in school. He will work on home work at lunch and in the car so he can have more time to do what he likes when he is at home. He has the discipline to work as needed. He likes to sleep and requires 8 hours a night.
None of us utilized a schedule or calendar to get things done. You will know if you over-schedule and then it is up to you to make the decisions on what to give up.
I specialize in that. I have a USNA plebe and he swears my planner and system is a major reason he is doing well at the academy right now. **LINK REMOVED** I work mainly with college students but the basics are the same. I have a few colleagues who specialize in high school. You can do it without paying someone though, you just have to be proactive and be motivated. The Cal Newport book is fabulous - geared toward college students, but useful for high school. There is a single chapter on time management that, if you read only that chapter, you will have gained great insight.
Backdating is another wonderful skill. Mark the due date, then mark YOUR due on a calendar, then work backwards. Set yourself daily and weekly goals based on what you need done (draftn study group, library research time), until you get back to today. You'll be able to prioritize every major assignment easier this way.
Lots of good advice above, but Ill add a more basic element. As a student, the best thing you can do for yourself is be present and fully engaged during class. That means sit up front, pay attention, ask questions if something is not clear. If you already do this, great, but far too many students don't focus during class and have to spend more time outside of class studying. Also, if your teacher gives you class time to work on something, use it to do your work. Save yourself HOURS of catch-up time each week by effectively using your class time!
One more important tidbit. Most students do NOT utilize professor's office hours nearly enough.
My DS was struggling with a particular English class and of course he was being annoyingly stubborn (don't know WHERE he gets it from!) about his studying techniques. I finally got him to visit his professor during office hours and get tips on what he was doing wrong on his writing style. The professor told he exactly what to do to get a better grade.
He salvaged a B+ in a class that he was getting a C- in and was greatly relieved.
Use the office hours. Your professor is bored and WANTS you to visit. (Likely falls in the urgent and important quadrant).
There's been a lot of great advice on this forum, but as far as time management questions go, you'll be just as well off reading professionally written articles on Google. (No offense to anyone on this thread)
While you can buy someone's book, read all sorts of online articles from people with impressive sounding titles or follow some complicated 'process', time management is not a one-size-fits-all prospect and you aren't going to find any magical solution. Be organized, know how to prioritize and know how much you can take on are basics that apply to everyone. That also means knowing when to say 'no'. Some clubs/activities can eat up a lot of your time for very little benefit. Each school varies and only you know what your interests are, what you are good at and where you can best contribute.