Use exclamation points sparingly, and never more than one at a time. They’re like high-fives: A well-timed one is great, but too many can be annoying.
Exclamation points go inside quotation marks. Like periods and question marks, they go outside parentheses when the parenthetical is part of a larger sentence, and inside parentheses when the parenthetical stands alone.
Never use exclamation points in failure messages or alerts. When in doubt, avoid!