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

• Berlin is BIG. We're talking a city made of 2 cities and with sooooo much history going on in one place it will take a while to get round it all. Make sure you have good walking shoes and take some supplies.
• Carry a card from your hostel when going out late to show the taxi/policeman where you are staying if you can't speak (German).
• Watch out (or avert your eyes) for naked people in public places. It happens.
• Lets be honest. There are no ticket barriers for the trains but there are regular ticket inspectors. You can expect a €40 fine if caught travelling without a valid pass.
• Padlocks on daybags. In crowds or displays keep your bag on your front and padlocked.
• Be aware on crowded trains and some buses 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 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!