As long as you're going to a major hotel and you're a newcomer to the city, the airport limo bus is the simplest, although not the cheapest option.

Depending on when you arrive, you may or may not get stuck in traffic on the way into the city.

In order to make the most of your visit, get a city guidebook and map before you leave.
You might also want to follow the links at the JNTO website, which contains PDFs of exhaustively described walking tours of the city.

http://www.jnto.go.jp