The "5 Flight Rule" refers to the first 5 flights. If any technical failures happen they usually occur in the first 5 flights. Keep the quad in close and - if possible - over high grass to prevent any damage. 

Things to pay attention during that time:

1) ESCs and Motor Temperatures

2) When you watch your flight recording pay attention to any rattling sounds.

3) Is the quad flying sideways, drifting or leaning in one direction?

4) All wires and connectors are inside the quad and are strongly connected.

5) Verify all props are secured and properly fastened

6) Check for heavy vibration in your FPV image or other issues in your video link.

Typical fixes, other than the obvious, contain re-calibrating ESCs and Flight Control, damping vibration-sensitive parts, separating receivers and transmitters or adding bandpass filters for interfering components.