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.
• Carry a card from your hostel when going out late to show the taxi/policeman where you are staying if you can't speak (Czech).
• Always ask for a receipt from officials and service providers such as taxis and ticket inspectors. Ask to see identification before paying any fines.
• 'Hawkers' or guys selling stuff on the street can get pushy so its best to ignore them and continue walking.
• Padlocks on daybags. In crowds or displays keep your bag on your front and padlocked.
• Be aware on trains and the Metro for pickpockets. Keep bags padlocked and worn on your front. Be especially vigilant on crowded trains and watch out for 'fake fights' designed to distract onlookers.
• NEVER put anything remotely important in those cargo pants pockets. Pickpockets love them best.
• NEVER take your daybag with passport, credit cards, guidebook, train pass, plane tickets and $1000 Nikon camera 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 box where you are staying.
• Ear plugs, flip flops and a sarong. The SAS would agree.
• 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!