I've never met a high schooler who couldn't benefit from this time management exercise.
Using a pencil and paper, map out a typical week of homework. Leave space for five weeknights (including Sunday), and two weekend days. Give yourself a night off (most people don't want to work on Friday night).
Make a list of all subjects that assign homework, and estimate the amount of daily and weekly homework for each subject. In this way, figure out how much work you really have per day, and per week, on average. Take your time with this. Use the rule of 33 --assignments take one-third longer to complete than you usually think -- and make sure to allow for extra time to study concepts that require further review. Frequently, the best studying involves taking time to think about a larger idea, or taking time to clarify details that underlie the larger idea.
Now figure out how much time you actually spend doing homework each night. This is your reality check. Turn over your piece of paper and ask yourself what time you usually finish your work. Take a look at how you typically spend time, and decide if you are happy with the way you study. A picture should emerge, and it is this: how you would best like to do your homework.
Consider this possibility, if you do not already work in this way. When you get home from school, take a short break. Choose an activity that you will enjoy, such as sitting outside, but keep it short. Then begin homework and work steadily until it is done, stopping only for dinner. Take whatever free time you have only after all homework is done.
Watch your life improve.