For years, one of the best tools for checking correct usage of a particular word, how to punctuate, the difference between i.e. and e.g. has been the Chicago Manual of Style.
This is the style guide that many publications use to ensure consistent writing and formatting.
It's a great tool to have at your elbow whether you're a writer or editor, but you no longer need to weigh down your bookshelves with the brick-sized tome. It's now online, and anyone can sign up for a free one month subscription to check out the full version, including searchable access to the complete manual content, and along with the latest opinionated responses to questions such as whether to capitalize after a colon (answer=sometimes yes, sometimes no), and how to number pages on a manuscript submitted to an agent or publisher. It's well-worth the $30 annual subscription fee if you want the full monty.
But the free content of the site is well-worth bookmarking - and using often.