Ensure all electronic components which are sensitive to electrical noise (gyro and receiver) are placed away from the components which generate electrical noise (motor and speed controller).
Try to route wires to/from electrically noisy components (ESC power, motor, and control wires, also all switching BEC wires) away from other wires. A good strategy is to route the noisy wires on either the left or right side of the heli, and all other wires on the other side. Do not coil excess wire. These coils of wire will act as an antenna and will amplify the generated or received electrical noise. Bundle the wire in an S-pattern instead.
Ensure the expensive electronic components (such as the gyro and speed control) are located where they will not be easily damaged in a crash.
Ensure all wires are securely fastened, especially the wires from the gyro. Dangling wires may cause tail wag problems.
Put a strip of tape over the receiver crystal to ensure it will not vibrate in flight (which may cause glitching) or fall out of the receiver.