Try advertising on other sites. Like where it says “Your AD Here” or something.
Also you can send out a monthly newsletter (that usually gets members active on some sites)
Try installing this plugin:
New User Email Set Up
You can set it up so that it email’s the newly registered user their:
- user name
- email
- password
and/or your:
- site url
- blog name
- login url
Hope this helped.
