I have found through my personal experience that though each student has a separate style of learning, the most universally helpful study skill is to write down your own notes. Repetition is essential to memorization.
This works in all subjects, too – memorization is key!
History: This is the most obvious one; you need to know dates. You say your not good at it? Okay then, what you need to do is sit down 20-30 minutes a night and bounce information off someone else – a parent, a sibling or a friend.
English: (Vocabulary) MAKE Flash Cards! This is the best way to study. Even just making them is a good start, but you should still go over them a few times every night.
(Grammar) This one you’re going to have to follow the old “practice makes perfect” idea. Simply write down some sentences with no punctuation and then go through and place it in yourself.
(Spelling) This is where repetition is the only way – going over it again and again.
Math: What you need to go over here is formulas. If you know those, it’s just plugging in numbers, which does not take much thinking at all.
Science: No matter what level of science, this is about the same as history – you need to work memorization. For biology and anatomy you need to go over the parts of the body of both humans and animals. For chemistry you definitely need to go over the periodic table of elements.
Physical education: This I admit you do not have to study for, but it is a required class where I live and it’s something that comes a lot easier if you keep your body in shape. Which leads neatly into the concept of forming habits, which are very useful.
The best way to accomplish any of these goals is to form them into habits. This means that you need to consciously make an effort at these tendancies so that once you have set them into a sort of routine you will be able to perform the tasks and make them work in your favor with no problems at all. You will perform these actions involuntarily and they will be second nature, much like brushing your teeth or eating dinner. This will insure that you will not fall behind in your studying and will definitly be ready for any test that comes your way.
For anything else the same concept applies: If you’re going to learn something and remember it, the best thing to do is to follow the concept of “Practice Makes Perfect” or at least better prepared.