I have reached 1500 with turn based.

That is thanks to tactics trainer, a tiny bit of endgame study with ebooks and plain practice.

How should I study chess to improve more?

I have a lot of schoolwork right now so time is scarce until the weekends.

Any ideas?

Thanks ~ LOB

Buy a program such as Rybka, Fritz, Shredder, etc.  Compare your games to what the program would play and find out what mistakes you are making.

Programs succh as Fritz and chessmaster are supposed to be good. Read books in the areas you stuggle endgame, etc

You asked such a great question. 

It is the same question I have been working on for decades. Here is my humble opinion.

In my experience, the answer is different for different people.  For example, if you are new to chess, then you have few wrong ideas deeply ingrained in your mind.  If you are like me and have been playing for decades, you may have to find out what your deeply ingrained wrong ideas are, and then erradicate them. 

One of the risks of study is spending time studying the wrong information that does not yield results.  If you do that, you can become discouraged and quit studying altogether.  Another risk is spending time "studying" when, in reality, you are only entertaining yourself. To avoid these pitfalls (and more), it is best to find a teacher you can meet face to face to facilitate your learning.  Your teacher should be at least master strength and should possess solid teaching skills as well (he/she should have a reputation for helping folks to learn). 

In the meantime, try the "Novice Nook" by Dan Heisman:

http://www.chesscafe.com/heisman/heisman.htm

His column deals well with this subject.  Check out the archives there for a valuable source of training material that is easy to understand and to the point.

Good Luck!