The job of an auto mechanic is both to repair an engine and to prepare it for optimum performance once it leaves the shop. Regular maintenance is important for any kind of vehicle, from a minivan delivering kids to school to an Indy 500 race car surging to a finish.

Working on a portfolio is a lot like maintaining a car: you have to evaluate what's there, decide what needs to be fixed, and then use the proper tools and skills to enhance performance.

Much of the work you've done on your portfolio so far has focused on revising and editing—getting all the right parts in working order. As a last task, you're going to look through your work once again and focus on proofreading. While you may have completed the proofreading phase of the writing process, true proofreading is never really finished, just as the work on a race car isn't over—even during a race!

Once you're sure that you've chosen the right words and arranged them in the best order, you should focus on mechanics, the aspects of writing that affect how the piece looks on the page. These include spelling, punctuation, capitalization, and abbreviations. Where to place commas is a skill that is challenging to many writers, regardless of how long they've been writing.

Some comma rules are easy to understand and follow. Click each of these reasons to use a comma to see an example of the rule in action.

Use commas to separate words, clauses or ideas in a sentence.

My dog Sully is cute, smart, and obedient.

Use commas to set apart dates and parts of dates.

July 4, 1776, was an important date in American history.

Use commas when integrating direct quotes into text.

"When you leave the house," my mother yelled after me, "don't slam the door!"