To get the best performance out of the Crazyflie we recommend you to optimize it. Below you will find some tips

Vibration is one of the biggest reasons the Crazyflie performance is degraded. Vibration effect the gyro and accelerometer measurements making them more noisy and inaccurate. Vibration is mainly caused by unbalanced propellers but can be caused by a bent motor axis as well. Balancing these small propellers is extremely hard and we are still searching for a good way to do it. An easier way to get balanced propellers are to sort them and categorize them according to their vibration. This can easily be done by using the spare motor and a normal 1.5V AA battery to power it while testing each propeller. After this has been done use the propellers with the least vibrations.

Getting the centre of mass(CoM) in the centre of the Crazyflie will improve the performance as it means the motors will be equally powered when hovering on one spot. That will give maximum control head room for the stabilization and best efficiency. So when you attach the battery do you best to get the weight centred.

Your copter is facing forward when both the red and green LED are doing so. However, that might be a bit difficult to determine, especially if you are looking at your copter from below (since it's flying higher than your heade). To compensate for that you might want to mark the motor arm of M1 with some colored tape.