Buy a c language reference , user guide or tutorial book. It will be good if it has a compiler or interpreter software along with it in a DVD/CD.
Read the book and at the end of each topic, try the examples given in the book or the DVD. It is a must to write algorithms, flow charts carefully before writing programs. Test the programs on line with the DVD or on the Internet sites where c programs are compiled and executed and results are shown.
This is the simple way.