As they say in the real estate business: location, location, location! Rome was centrally located. It had great amenities, including access to seas and rivers for transportation. It was had good soil and a strong, sturdy people. Add that to Rome's ambition and boom, ready-made empire.
Certainly the position of Rome on the coast was a great bonus to Rome's initial development. Having ready access to the Mediterranean was vital in terms of both trade and military conquest, as Rome was able to effectively marshall troops and also allow the trade of Rome to develop.
A couple of important geographic factors were the less rugged nature of the hills on the Italian peninsula and the accessibility of the rivers. These factors encouraged overland trade and a unification of the separate groups of people. Compare this to Greece with more rugged mountains, less accessible rivers and more obstacles to the unification of groups.
The major geographic factor that led to the rise of Rome was its location on the Tiber. It was located at a ford in the river at a point that was more or less in the center of the peninsula. This meant that it could control trade routes (and get money in tolls and such) that had to cross the river at that point.