Onsen in Tokyo

What is the proper etiquette when going into an onsen? Can a lone female go in there? I want to try it but don't have a clue about where to go and what to do!

Thanks!

Onsen etiquette:
http://www.onsenjapan.net/onsenbasics.php
http://www.infomapjapan.com/hstore/200512-spfeature.phtml

Ooedo Onsen Monogatari in Odaiba, Tokyo
http://www.ooedoonsen.jp/higaeri/english/index.html

The instructions about taking a bath are rather strange on the suggested page:
http://www.onsenjapan.net/onsenbasics.php

I disagree that you should use a lot of soap. In some traditional baths out in the nature, you may even be forbidden to bring and use soap.

Also, according to the Japanese way of bathing, the use of soap is most effective not before entering the bath, but only after taking a first soak.

Just a rinse is sufficient before entering the bath for a first soak. If you are excessively sweaty or dirty, use your small towel to clean yourself and/or take a short initial shower.

Here is another guide on how to use baths:
http://www.japan-guide.com/e/e2292_how.html