This problem often seen in students. Students say they get bore after studying for sometime.Here is the method which i applied on my self. This showed a good result. 1. Select a peaceful place with plenty of fresh air. 2.Always use a chair or stool to study as it protects us from laziness and hence from sleep. 3. Select a limited work or pages or topics to be covered in a short span of time. The selected pages or topics should be less than your average speed of reading. e.g. if u can read or learn 8 pages in a hour select 6 for hour.
4. Drink water whenever you feel sleepy. Can also try coffee or Soda containing caffeine and peppermint toffees or chewing . Chewing also keeps brain active by supplying blood.
5.Read and learn as you are not a student but as you are a teacher. Explain each every thing to yourself in the language you like most. Treat nearby area and walls as students.
6. Listen some music after some pages or topics as a reward.
7.For numerical or practical subjects listen some soft music in slow volume along with study.
8.Feel the importance of each and every topic in your life. Try to get examples for each topic.
9. Correlate each topic or paragraph with something. Like while studying something about business try to correlate it with your own business or friend's business.
10.Make songs or poems of difficult lines you are unable to learn.