No staying after school for projects - bad association!
No making friends with worldly kids when you live at home - unless they agree to study and/or attend meetings with you.
No decorating with corn stalks at your door in the fall - too worldy/resembles Halloween
Heres an old one that had since quite being practiced but used to be:
not putting your name on a gift at a baby/wedding shower - considered a lack of humility to show what you gave.