I need advice on three things

First my engine RPM decreases rapidly as I leave clutch in the first gear. (both on CNG and Petrol)

Secondly i feel jerks in the engine at low speed (like 20kph in 2nd gear)

Third, when i apply brakes, i feel some sort of vibration in the car.

Kindly guide me what do i have to do to get rid of these.

Car : Honda City 2007