Courtesy of the CDC:

Wear your Mask Correctly

Wash your hands before putting on your mask
Put it over your nose and mouth and secure it under your chin
Try to fit it snugly against the sides of your face
Make sure you can breathe easily
CDC does not recommend use of masks or cloth masks for source control if they have an exhalation valve or vent

Wear a Mask to Protect Others

Wear a mask that covers your nose and mouth to help protect others in case you’re infected with COVID-19 but don’t have symptoms
Wear a mask in public settings when around people who don’t live in your household, especially when it may be difficult for you to stay six feet apart
Wear a mask correctly for maximum protection
Don’t put the mask around your neck or up on your forehead
Don’t touch the mask, and, if you do, wash your hands or use hand sanitizer to disinfect​

Follow Everyday Health Habits

Stay at least 6 feet away from others
Avoid contact with people who are sick
Wash your hands often, with soap and water, for at least 20 seconds each time
Use hand sanitizer if soap and water are not available

Take Off Your Mask Carefully, When You’re Home

Untie the strings behind your head or stretch the ear loops
Handle only by the ear loops or ties
Fold outside corners together
Place mask in the washing machine (learn more about how to wash masks)
Be careful not to touch your eyes, nose, and mouth when removing and wash hands immediately after removing.

I have to admit that while I did most of these correctly there were a number of places where I have been a little sloppy.

I also have a mask with a valve that I just learned the other day is not terribly effective. 

I have others now and I plan to wear them properly from this day forward.