Some tips for folks who don't want to be public all the time:
- Make "who's in your circles" private. Go to https://plus.google.com/me/about/edit/nv
and select "Your circles" instead of "Anyone on the web".
- While still editing your profile, whenever you edit the individual fields on your profile, you can choose who can see it. I chose only to share my phone number with family for example.
- When sharing a post, choose specific circles. And don't feel like you have to do "Your circles" -- pick specific circles.
- Use "View Profile As" (after editing) to view the profile as someone else to see what they see.