My quad is not flying ,everytime i arm and increase throttle,instead of lifting vertically up, it flips on the ground. I think i need to tune pid's...

Flips can be caused due to wrong wiring orientation of the ESC with the Flight controller. Check the frame motor layout and connect accordingly

No bro the wiring is correct,the motors are spinning in correct direction as required , and i have wired them according to multiwii. Pls any help..

If motor layout and wiring is correct, you should do esc callibration and radio callibration properly. The radio stick mid points for AER channels should give close to 1500 ms on the multiwii flight status window.