My friend and I planning a week of travel in Japan and are thinking that 3 days is good for Tokyo. Hoping to see as much as possible in that time and wanted some tips/advice on where to go and what to see. Friend big sports fan so hoping to see some baseball or sumo if possible. Looking around on the internet but not sure where to base ourselves whilst in the capital.
When are you going? Sumo tournaments only happen a few times per year, and only three times in Tokyo.
For sure, see the Asakusa shrine, the Tokyo Museum and Ueno Park (close to the shrine, can be seen in the same day), the Shinjuku and Shibuya neighborhoods, and the Akihabara electronics district.
It's best to base yourself in Shinjuku, as Shinjuku station is nearby and thus, many metro lines and the JR East Yamanote line, which circles the perimeter of the city center. It also helps to serve as a landmark because getting lost in Tokyo is a given, not a possibility.
Shinjuku has lots of nightlife and cheap eateries. It's a great place to stay.
Be also sure to see Meiji Shrine and Omotesando (close to each other) as well as the up-market district of Ginza on a Sunday. Shinjuku is a great place to base yourself but if you're on a budget I've heard Asakusa is also worth looking into because there are many foreign guesthouses, although it will probably be a younger crowd. As for sumo, Emily is right -- events take place every odd month and come to Tokyo only 3 months (January, May, and September) so it really depends on when you visit (http://www.furthereast.com/japan/sumo/). You might have a bit more luck with baseball although the season is ending now and doesn't start again until April.