If your job involves using a computer and you have a company email address, you should have a writer’s style guide nearby at all times.
The best are:
AP Stylebook (published by the Associated Press)
MLA Handbook (published by Modern Language Association)
The Gregg Reference Manual
For federal workers, the most appropriate might be the GPO Style Manual (published by the Government Printing Office), which lists style and grammar guidelines approved specifically by the federal government.