Progressing through all the steps (check-in, baggage check, and security) can take several hours. Be sure to arrive at the airport with plenty of time to complete all of the steps required to board your flight.
For international travel, it is wise to arrive at the airport 3 hours prior to departure (2 hours for domestic travel). International flights often start boarding 45 minutes to 1 hour prior to the departure time to account for Immigration and Customs.
Think about the items you want to take with you, and create a packing checklist.
Pack your luggage carefully so as not to forget anything.
Check your Flight Status. On the day before your flight and also a few hours before you leave your house on the day of your flight, check the status of your flight on your airline's website. On their homepage, look for a "flight status" link.
If you have a connecting flight, then find out the gate number for the connecting airport so that when you land you know where you need to go. After you de-plane, you may need to go to different terminal to find your gate. You may receive your boarding pass for the second flight ahead of time or need to acquire it when you arrive at the new airport.
If you miss your flight before you have gone through ticketing or security, ask your airline's ticketing desk for help. If you are through security but miss your flight for some reason, ask your gate agent for help.