I actively resent having a Google+ account. It's a bloated desert of half-finished ideas. Even the Google employees I know seem to have stopped using it. It's a necessary evil when dealing with Google products, sadly. I haven't used it in months and my profile tells people not to contact me there.
That doesn't stop all manner of spammers from adding me to their "circles" - which, in turn, causes an obnoxious little notification bubble.
Ok, so if you have to have a G+ account (for YouTube, location services, or other reasons) - here's how you can make it totally private! No one will be able to add you, send you spammy links, or otherwise annoy you.
You need to visit the "Audience Settings" page - https://plus.google.com/u/0/settings/audience
You can then set a "custom audience" - usually you would use this to restrict your account to people from a specific geographic location, or within a specific age range. In this case, we're going to choose a custom audience of "No-one".
Check the box and hit save. Now, when people try to visit your Google+ profile - they'll see this "restricted" message.
NB - content you've previously posted publicly may still be visible.
Dear Google - you "sunsetted" Reader, Latitude, Code, and Glass - it's now time to do the decent thing and put G+ out of its misery.