It depends on your interests. Tokyo has many attractions and it is so wide.
There are historical restaurants and dessert places (Japanese style cafes) so visiting these places might be interesting. Such as Oogi Soba in Asakusa (soba restaurant), Hatsune (Japanese style cafe) in Ningyocho, etc.
You can explore around newest shopping malls such as Ginza Six in Ginza or NEWOMAN in Shinjuku. Those are the hottest places in Tokyo right now.
Go up Tokyo Tower or Tokyo Sky Tree to get the great view of Tokyo city. Night view is especially amazing.
Visit authentic bars. Ishinohana in Shibuya serves great cocktails. Exploring around traditional Izakayas is another fun nightlife activity.