At the leader selection screen, press A, then select your leader. Now, on Controller 1, hold Start and press A to start a new game.
This code is to be entered on the title screen where you select the number of players (1 or 2).
At the title screen, at the player selection menu, hold B and press Left, Right, Right, Left, Down, Up, Up, Down.
During your turn, enter the map mode by pressing Select, then hold Up + Start on Controller 1 and press Select again. This will leave you with only one move to play till the end of your turn.