Leonardo da Vinci once apparently said 'Just as eating against one's will is injurious to health, so study without a liking for it spoils the memory, and it retains nothing it takes in'.

Generally, if you don't feel motivated to study, while you are studying you will be wasting your time more often than not!

If you are studying something and you don't feel like studying it or your heart just is not in it, the best thing to do is STOP STUDYING!!! ... and then re-examine WHY you are doing it!

Think about what it is that you are going to be able to do AFTER the study is over. Think of all of the wonderful things that you will be able to do if you get the results that you want.

Concentrate especially on the positive things that are coming up. Don't simply try to scare yourself into doing it. Fear is not going to get you into the right mental state for optimal retention of information.

On the other hand, finding that reason to be positively interested in a topic will put you in an exploratory mood state and that is ideal for learning.

If you are a little tired, use a natural wake up method such as an exercise break.
Get out in some bright light and smile at someone in a crazy way. DO SOMETHING WHICH MAKES YOU SMILE.

Another thing that can add to your motivation is to actually plan rewards for yourself along the way. Little things that are just for you are the best. Make sure you have fixed points that you can mark yourself against to decide if you get the reward. Make the reward itself very specific. For example... after you have done a past paper or revised a certain amount of material, reward yourself with a swim at the local pool.

Suggestion: Don't simply reward yourself after a certain time. Reward yourself for a certain amount/volume of quality work.

One of the best motivators of our time, Anthony Robbins believes the way to motivate yourself and get things done, is to...

1. First get disturbed about what you are not getting done. Specifically think of why it is disturbing... really get very disturbed about it! Write it down.
2. Work out what you think should be getting done. Write it down.
3. Plan exactly what it is that you do want to achieve, setting yourself very specific and measurable goals to meet AND do something immediately to start yourself along the path to success.

There are many other important steps... If you really want to get motivated, I would really recommend you check his products out!