These are some of the lessons I have learned while traveling.
Pack smart and only take what you need. Then unpack 20% of that.
Expect things to go wrong because they will. Delayed flights, cancelled flights, bad weather and more are all part of traveling. Things are going to go wrong just pack a good book, fire up the computer or have a chat with others at a bar and it will eventually get better.
No matter what, do not follow the pretty girl downstairs to the club in Piccadilly Square London. Just trust me.
There is no real need to pack loads of cash, ATM's are everywhere.
Let your bank know what countries you will be traveling in or they might think your card is being used illegally and cut off the funds.
A group of little kids crowding around you are not always just curious. Sometimes they are skilled pickpockets.
German police don't have much sense of humor.
An extra large t-shirt in the Philippines is only extra large if you are a teenage girl.
In Thailand when they tell you your meal is a little spicy, they lie.
Don't be so aloof. Talk to everyone, the waiter, the hotel clerk, shop keepers and even strangers. You meet some really good people and they can give you insight into the area others will never discover.