On the vacation season, the airports and the airplanes are always crowded of people, so it's much more likely to happen a problem, like missing the flight because you're late, or the canceling of the seat reservation for any reason. There are some tips that could avoid most of those problems.
-Reconfirm your plane reservation
It's not good at all to pack your luggage two days before a flight to Europe. Prepare yourself to come to the airport two hours before traveling and see if your reservation wasn't confirmed on the airport sistem. For precaution, you have to check if your reservation was made successfully two weeks before the flight, and again two days before it, just to confirm the departure time.
-Check in online
Thanks to the technology, now can you not only buy your ticket from the internet, but also print it at home. The time that you are waiting to print the ticket wouldn't be wasted.
-Get there early
Anything you do for avoiding problems about the flight will not be worth if you get late at the airport. There's always a problem with the luggage or long rows for the check in, and you could miss the flight because of it. So, the ideal thing is that you come to the airport at least 2 hours before the flight to solve any possible last minute problem.