Just a quick and easy list of 15 tips that I use every time I travel:

Realize that it is no longer 1972 and airplanes are now big flying buses. Even business class is not what it used to be.
Do not screw around with immigration and customs staff. You will lose.
Book the most direct flight you can find, nonstop if possible. Keep weather in mind with connecting flights and watch out for connections in cities with multiple airports through different airports (airlines sometimes connect this way… watch it in places like London and New York)
I carry a US$ 100 bill for emergency cash. I have entered a country and all ATM and credit card systems were down. US$ can be exchanged nearly anywhere in the world.
Pack light. Pack light. Pack light. Pack light.
On long connections, many airport lounges are pay lounges and can be very comfortable and cheaper than a transit hotel.
Check, and recheck, required visas and such BEFORE the day of your trip. Some countries, for instance, require a ticket out of the country in order to enter. Others, like the US and Australia, require electronic authorization in advance.
McDonalds and Starbucks offer free wifi in most of the world.
Women you meet in bars never look the same at 8:00 am as they did at midnight (careful in places like Bangkok or Macao). There is a reason bars have dim lighting.
Security is asinine and inconsistent around the world. Keep this in mind when connecting flights. Always leave at least 2 hours for international connections or international to domestic.
Expats are rarely the best source for local information. Lots of barstool pontificates in the world.
Wiki travel and Lonely Planet are good websites to use for a “lay of the land”
Expensive luggage rarely lasts longer than cheap luggage, in my experience. Fancy leather bags are usually toast with air travel.
Buy travel insurance. A comprehensive annual policy is best and not that expensive.
Learning to say please and thank you in the local language is not that hard and opens doors. As does a smile and a handshake

Hope you find this list helpful!