What to do at evenings in Tokyo?

We'll visit Tokyo on March 17-22 and don't have yet plans for the evenings. Looking for good ideas about entertainment, restaurants, places to see, etc. We're 3 adults. Can you help?

Go out - anywhere - look at stuff, have a drink in a bar, talk to the people next to you.

If you are after recommendations, it might help to know where you are staying - Tokyo is a big place.

We stay at the Prince Park Tower Tokyo

The Prince Park Tower is very close to Tokyo Tower, so you may want to visit it. However, if you take subway from Shiba-Koen to Daimon, you can go up to the observatory of Sekai-Boeki-Center building (World Trade Center Building), which is the best viewing spot for Tokyo Tower. They say it is not so crowded so you can enjoy Tokyo's night view (including Tokyo Tower, of course) in a relaxing atmosphere.

Hanami night cruising, Sumida-gawa-river begins from 21 March.
http://www.suijobus.co.jp/event_cru/ohanami.html

Many thanks for the good ideas. We're looking for less touristic and more local (Japanese) way of spending evening.

Tokyo is just another international hub like London, Paris, New York.
I didn't experience anything traditional Japanese there other than Starbucks, Subways, Macdonalds.
And everything is overpriced.
I wouldn't spend more than one day in Tokyo should I be traveling Japan.
As a nature lover my favorite spots are Nagano, Ibaraki, Shizuoka.
Tokyo is also home to Japan largest foreign community plus Japanese who work there from other Prefectures making it quite unlikely to meet locals there.
From what you're saying Tokyo must not be the best spot for you, sorry.

Go to Shimbashi Station in the evening and walk around the watering holes and meet the salarymen while they decompress after work. You can go to izakaya there and strike up conversations with the usually reserved people who let their guard down with a little alcohol. They're also more likely to speak to you in English as well.

Visit Shinjuku "Golden Gai" pub/bar street and "Omoideyokocho".