When you're buying a plane ticket and the flight path requires a layover, double check that the ticket allows enough time for you to disembark the plane, navigate through the airport, and reach your next gate with plenty of time before boarding.
This is important, because sometimes when you book tickets, the airline will only leave you a small window of time for changing planes. It's up to you to gauge whether you feel you have enough time or not. Most of the time it will work out, but occasionally you may not have enough time to make your next plane if the layover is too tight.
This is especially true if the first plane winds up late for whatever reason. This happened to me on a flight to Europe, with a layover in New York. I had to run through the airport with a heavy pack and the airline almost didn't let me on the plane because I was late!
Also, take into account whether you might want to eat a meal during your layover. If you're really on a long-haul trek, spending a few hours in an airport might be good for you to get some exercise, eat a decent meal, and get to your flight gate in a leisurely fashion.