These aren’t regulations, just tips that everyone can voluntarily use to improve their onscreen clarity.
Put your light (or sunlight) behind or to the side of your computer camera so that you aren’t in shadow.
If you’ve stepped back from the microphone, project your voice in order to be heard clearly.
Unless your league has given you rules on how to sit/stand, try various positions to find the one you like best - sitting in front of camera, standing in front of camera, sitting on a couch, etc.
Don’t wear clothes that have thin stripes or clothes that are shiny because cameras sometimes distort how these fabrics look.
Look at or toward the camera. Don’t have the camera pointed to the side of you, above you, or below you.
At minimum, your head and shoulders should be onscreen without any part of your head being cut off.
Mute yourself before you burp/sneeze/cough into the mic.
Make sure your background, real or virtual, is crisp and clean.
Use an ethernet cable instead of wireless for stronger internet signal.
Test out your online platform the week before the tournament in order to become familiar and avoid glitches.