To think that there is one secret glorious trick for everyone to learn everything quickly - and then remember it all - is a bit of wishful thinking. There is no trick. No shortcut. The real obstacle is to find the perfect blend of concentration and relaxation that lets you absorb what you learn. And that blend is different for different people.
Find the mood that suits you
Some people prefer perfect silence. Some like the buzz of background noise of other people. Some prefer music. Find out what works for you. What lets you relax but doesn’t distract you. Go out to a coffee shop for a couple of hours with your books (that always works for me), change your surroundings now and then so you wont get bored. With technology now you can simulate pretty much anything - if you like the sound of rain and a crackling fireplace when you study you can find them on endless loops on youtube!
If you are studying chemistry, don’t keep worrying about all the chapters in all the other subjects that are left. In fact, don’t think about anything that would worry you and take away your concentration. In that moment only you and the material in front of you should exist.
Don’t cram. Don’t exhaust your brain. And for the love of God don’t stay up all night! Especially the night before the exam: Watch a movie. Listen to music. Read fiction. Let go of the tension. If you go into the hall, scared, dreading the paper you are done for. Relax.
If you are stuck at something, don’t panic. There is always an answer and a million videos and websites that can help you find it. If the text book isn’t working for you, take out the syllabus, find out what you need and find it somewhere else. It is true that some people understand better when they read something and some get it better when they watch a video, or draw diagrams. Find out what works for you.
Studying actually works when your brain is actively involved. Don’t expect it to understand things on the first try. Don’t expect it to remember things if it has only passively been fed by either just reading or just listening. So what does active mean? you should try to visualize the things you are reading about. Concentrate until you can see them happening.
Explain them to yourself without looking at the book. Draw them out. Talk yourself through it till it clicks. Again, whatever works for YOU!