You can go online

For concert and theater tickets, I usually buy them online. Most ticket outlets has their own sites, and try using eplus ( http://eplus.jp ) for their large selection among these.

The challenges with these sites are (i) they are only available in Japanese, and (ii) they require registration to make reservations. This combination makes reservations even more difficult because they don't work well with Google Translate (specifically and technically, use of Cookies doesn't work through Translate sites).

This should be still useful in some cases when you are not in Japan but you want to make a reservations, or simply you want to check event schedules.

Other popular ticketing sites:
Lawson Ticket http://l-tike.com/
Ticket Pia http://t.pia.jp/

Hope this helps.