My coworker Emma Lord suggested:
"The fastest way to ingrain a new behavior is to have it at the top of your mind. Ask people to remind you if they catch you touching your face, and if they ask you to do the same, look out for them too. Beyond that, try setting little alarms on your phone or your desktop to remind yourself, or put Post-it Notes in places you know you'll look often — the desk window you stare out of when you're thinking, your computer monitor, your vanity mirror, the kitchen table. Heck, invest in a temporary tattoo pen ($9.98) and write the words 'Stop touching your face' on your own hands, so you have to look at them every time you type. Make it easier by setting yourself up for success — you'll feel better if you get reminded before you do it than if you're beating yourself up afterward."
Check out her other suggestions here.