At the title screen where it says press start. Push in on the right thumb stick, then push in on the left thumb stick, then direction pad right, direction pad left, then L button, R button, push in on right thumb stick, push in on left thumb stick, direction pad right, direction pad left, L button, R button.
If done correctly a bar will come across the middle of the screen saying God mode activated. Then press the a button and start the game as normal.