As Amsterdam is relatively small and attractions are quite concentrated in the city center, you can easily walk from one place to the other. Plus, it is a great way to discover this charming city. Get a good map of the city: with all the canals, bridges and streets (that all look alike the first time), it can get confusing.  Also, make sure not to walk on bike trails and to check for bikes before crossing bike trails or streets - 

The streets and sidewalks almost all have some form of cobblestone or brick, so make sure you have sturdy walking shoes.  Any shoe with a very thin sole will not navigate the ups and downs of the uneven cobbles very well and stubbed toes are a real possibility for sandal wearers.  A note here for those with walkers/wheelchairs/scooters:  while there may be an elevator in the building, it is not uncommon to see one or two steep sets of 5-6 steps to get into the main level of a building.   It also can occur that a tram driver will not stop for a wheelchair or scooter passenger if the designated spot is already taken. 

Another option is of course to bike. You will see millions of bikes in Amsterdam and throughout the Netherlands. It is a great way to discover this flat city (and country).  Bikes can be easily rented at various locations, and locks are provided as well. This page ( Amsterdam Bike Rentals ) gives a list of bike rental shops in Amsterdam.

The public transportation system is very good with plenty of trams, bus and trains. See the section on public transportation.

Avoid at all costs to driving a car in Amsterdam: the street map can be confusing and parking is just impossible (there are a few expensive public parking in the center for the city though). If you come from another city (or country) by car and Amsterdam is one stop in your trip, park your car at the Park & Ride ( P+R) located outside the city and get into town for free by subway. Rate is Euro 5.50 per 24 hour.