Pick up a Tube map. Maps are available at almost any Tube station or plan your trip online ahead of time at the Transport for London website. You can sometimes even pick up Tube Maps from convenience or gift stores.
Buy your Tube ticket from an official ticket booth. If you plan to use the Tube more than once in a day consider buying a day traveler's pass for unlimited rides in a single day. Buying your travel pass at an "off peak" times will save you a couple of pounds.
Wear comfortable shoes. Sometimes the distance you have to walk from one platform to another is further than you might think.
Expect to see plenty of "buskers." Signs ask you not to tip these pan-handling musicians, but some are pretty talented and definitely worth a coin or two if you can spare it.
Keep your ticket accessible. You will need to show it occasionally to Tube attendants or run it through a machine to operate a turnstile.
Mind the gap. There a small space between the boarding platform and the Tube car. If you ride the Tube more than once you have trouble getting the repeating message, "Please mind the gap between the car and the platform," out of your head. Since you won't be able to shake the slogan free from your mind don't be surprised when you give in and buy some of the trendy and plentiful "Mind the Gap" merchandise.
