Grammar Smart 3rd Edition - Princeton Review 2014

C. The Exclamation Point
PART 4. Punctuation

Exclamation points are used for emphasis! Excitement! Surprise!

Rules For Exclamation Points

1. Use an exclamation point after an exclamation.

Get lost!

Aha!

We won!

2. Don’t get carried away with exclamation points. The only error generally committed is using an exclamation point to try to give writing more emphasis than it deserves. And never use more than one!