What you need: A Nexus 7 ,a PS3 or Xbox controller(or another game controllers), a USB OTG cable to turn the micro-USB connector on the bottom of your Nexus 7 into a full-sized USB port, a mini USB to USB cable for PS3 .

Step 1. Connect USB OTG cable to the micro USB port of Nexus 7, the other side with the mini USB to USB cable or wired pad.
Step 2.Plug in the PS3 controller or Xbox controller. With luck, your controller will turn on and be automagically detected by the Nexus 7
Step 3. Press the controller's Xbox 360 or PS3 home button, when fiddling with the analog stick while on the app menu, you should be able to move between apps, and open the games like with the Y (Xbox 360) or X (PS3) button.
Step 4.Load up a compatible game like Dead Trigger, Asphalt 7, or OnLive. You can start to find the game with Nvidia's TegraZone app, which will point you towards many a fine Tegra 3 optimized title including joystick support.
Step 5. If your game is not optimized for controllers, you can use the gamepad with emulators to let you manually assign different button taps and analog stick wiggles to in-game inputs.