Make things interesting. Logical arguments will not give you motivation to study. Thinking that if I study hard and get into a good university and get a good job, etc., will not interest you. Love what you do. Try to find the beauty of every subject, and most importantly try to link it with the events of your life and things that interest you. This linking may be conscious (ie. performing chemical reactions, physical experiments or manual mathematics calculations in order to prove a formula) or unconscious (eg. You go to the park and look at the leaves. Then you think to yourself, Hmm, let me review the parts of the leaf we learned in bio class last week). Even though this might not sound the most ideal method for theoretical subjects such as English, use your creativity to make stuff up. For example try to write a story with all subjects starting with S, all objects starting with O, and no verbs containing V.