Some users (like myself) don’t have an option to disable their webcam and microphone in their BIOS and don’t want to mess about with the insides of their computer. The next best thing to this would be to disable the drivers for the webcam and microphone so they cannot be used. It would be good to add steps for these to the Hardware Threat Minimization guide on the wiki.
For Linux, you can add files to /etc/modprobe.d to blacklist the modules. Add
blacklist uvcvideo to disable your webcam driver. The driver for your sound card will be in /proc/asound/modules and you can add a file in /etc/modprobe.d for it e.g.
For Windows, you can disable them from the device manager.
Steps for other operating systems should also be added.