These won't make you into an SAS commander but they may help avoid some difficulties as you travel around.

• Pay money onto the dishes by the cash register. Never put it into the hand of the cashier. Likewise they will put your change into the dish. Try to pay with exact change.
• Don't play football with the streetkids, unless you know you have absolutely nothing worth losing on you.
• Carry a card or flyer from your hostel when going out late to show the taxi/policeman where you are staying if you can't speak (Spanish).
• SIESTA. It works all year round and is a 3 hour break in the afternoon between 1-4pm. All the shops close except larger department stores and maybe a sandwich bar or two. Very handy in the height of summer.
• Be aware of distractions from individuals such as asking you for directions, bird 'poo' on your back, gypsies with flowers or dropping items in front of you.
• Try to blend in a bit with the locals. Don't wear bumbags or wave tourist maps around too much.
• Put padlocks on day bags. In crowds or at displays keep your bag on your front and padlocked. Do not hang over the back of your chair in an outside café.
• NEVER put anything remotely important in those cargo pants pockets. Pickpockets love them the most.
• NEVER take your day bag with passport, credit cards, guide book, train pass, plane tickets and $1000 Nikon to dinner and the pub. Take a disposable camera and as much cash as you will need. The rest can stay in the safety deposit boxes where you are staying.
• Ear plugs, flip-flops and a sarong. The SAS agree totally.
• One noisy plastic bag only in your pack. This avoids someone hurling abuse and bottles at your head at 6am when you are leaving your hostel room for the airport.
• Keep an open mind!