It took me 3 weeks to study for CFI written and just passed FOI, FIA, AGI!! and starting cfi training from next week.

I would appreciate if someone can give me any suggestions for training material.
Is king DVD CFI cource worth to spend?

ASA is a lot cheaper but their speakers make some factual mistakes you should watch out for. The production quality is a bit on the sloppy side but the price is very good (something like $75). King videos are better made but require installation on your computer to defeat copying which negates using them for reference purposes after finishing the course and they cost a lot. I would not get them unless you are loaded and your school requires them.

I used the King CFI checkride videos to prep for the checkrides and the ASA Private/Commercial/Instrument books to build my lesson plans. I thought the King checkride videos were especially good prep for the CFI oral. The ASA books are good because they tend to go more in-depth than the Jeppesen books.