modifying destop game into android/ipad touch screen game

Hello and Hi,
         I am developing a shooter game
game uses arrow keys to move the shooter 
now i want to make it playable in android tab or 
ipad.
      i things i should consider first
and what should i change.and how..
i think i need to use any joystick control in my game. please give me any reference for joystick use.

i tried deploying the game in Ipad and android tab
only mouse-click event is mapped to touch event.

again mouse move,and character move is not working as i cant give input by keyboard.

please give me hint..
thanks in advance..

You will want to check out the mobile controls, just import the Standart Assests (Mobile)* package and take a look at the First and Third Person Controller prefabs and, of course, at the Character Controller scripts from the package. It’s all is pretty straightforward from there.

*(Assets → Import Package → Standart Assets (Mobile))