Once upon a time I was at UC Berkeley working two part-time jobs, an internship, and taking 16 units while still getting eight hours of sleep a night. Effective time management coupled with efficient studying habits in an (arguably) easier humanities major made this possible.
Things You Will Need
Just your regular class materials
Don't read everything. In fact, if you can help it, don't read anything at all until step 3 when you know which readings actually matter. If you must read, read only the introduction paragraph, the conclusion, and all headings or words in bold in between. That should give you a good outline/summary of what the author trying to prove or tell you and how they try to prove it or explain it. Everything else is just detailed examples or supporting argument.
If you need to participate during discussion sections, find one of the broader or longer examples from one of your required readings for the week and use that as your talking point. You should have a decent idea of what the readings were about from reading the introduction paragraph, the conclusion, and all the headings to give general feedback too.
Go to lecture and take notes. This is a lot easier to do if you have a professor that lectures in clear outlines but regardless, take notes. Pay attention to which readings they emphasize and key ideas, words, or topics that they constantly refer back to so you know which readings to focus more on and what exactly about those readings is important to know for the midterm or final. The more they talk about something, the harder you should study it. Forget everything else.
papers on specific topics, use the syllabus as a table of contents to find in which readings your relevant information is located. Find the relevant section in that reading by skimming headings or bolded words. If it's a book, just look in the index for key words and what pages it references. Read only what's relevant and get writing.
When you study for your final or midterm, study your lecture notes to see what topics, readings, and key words are emphasized and use that to try to guess what sort of essay questions your professor will ask. Find broad examples or arguments you can apply to answer a variety of different essay questions. Make a list of key words and their definitions. Memorize them.
There you have it - how I got through college without actually reading maybe 80% of my assigned reading. If you actually want to learn though, you should probably just set aside more time to study and read everything.
Tips & Warnings