A friend of mine gave me the following advice:
1. Don’t put in writing what you can say with your mouth.
2. Don’t say with your mouth what you can imply with a gesture.
;-)
The long version:
1. Do not write what you can say.
2. Do not say what you can nod.
3. Do not nod what you can wink.
4. Do not wink what you can smile