Start off with the subject you find most difficult first. This is going to make everything easier on you in the long run.
Step2
Read about your subject. Re-read, and read again. Remember, your goal is to absorb the information, not go on overload, and forget it. Due to our attention span, study for 45 minutes, and take a small 15-30 minute break.
Step3
You should study also using all of your senses. This is a way to help you know, and retain your information. Example: When you are studying, focus first on seeing what it is that your material is saying. Next, focus on hearing your material, record it, then listen. Your next step would be to feel your material, what would it feel like if you where flying that plane that you are studying about? What ever your case may be, what ever it is that you are studying, feel it. If you can not decide on how you are going to feel your material, then put a pencil in your hand, and twirl it as you read. What you are doing is stimulating your mind in different ways. It will help you grasp your subject.
Step4
If you can, write down some questions about what it is that you are studying, and answer them, repeat all of this, until you are comfortable with your material. Then you may go through one of your text books, and answer the questions that they have to ask. Need more help? Read answers on your subject, and study the answers until you can grasp how those answers came about. Do this, and make your own up as well.