There are two teams which participate in World Sudoku Championship. One of them is selected through Indian Sudoku Championship(ISC) and the other through Times Sudoku Championship(TSC). The selections for ISC are already over and it will be held in Chennai on 29th of July. The only way left for you is through TSC. The dates of TSC have not been announced yet. Keep track of the LMI forum or Times website for updates regarding TSC.
The participants of ISC are selected through Sudoku Mahabharat. The Sudoku Mahabharat for this year is already over and the participants have been selected. So, one cannot participate if not selected.
But this is not a dead end. Just keep track of the website and particiapte in the regular competitions held here. Till the time the next competition begins you may download and enjoy previous competition sudokus http://logicmastersindia.com/lmitests/downloads.asp