Common issues:

• follow jitter → consider LateUpdate;
• camera clips through walls → use Raycast/SphereCast;
• unlimited vertical rotation → clamp pitch;
• harsh movement → use SmoothDamp/Slerp;
• multiple AudioListeners;
• Camera.main returns null → check the MainCamera tag;
• incorrect mouse/gamepad sensitivity handling;
• mixing player yaw and camera pitch incorrectly.