What You Need to Know About Air Travel.(Ahead)

Byline: Sean O'Neill

1. The aisle seat you thought you had? Gone. Your seat assignment isn't a done deal until you're holding a boarding pass, even if you selected a seat when you bought your ticket. (One exception: Northwest Airlines is testing guaranteed reservations for aisle and exit-row seats for a fee of $15 for each leg of the flight.) Boost your odds of receiving your preferred seat by checking in online. Most airline Web sites allow you to check in within 24 hours of your flight's departure.

2. Try saying "pretty please." Airlines give their airport agents discretion to assign seats and make other decisions. Use them. Last year, five months before …