When you're starting out on Google+ (or any social media), or even if you've been using it for a while, you need to set Goals. Why? Well.....
Setting simple daily/weekly/monthly goals will help you measure how far you've come and what you have left to achieve.
Start with something achievable and build up.
Break down the social actions that you're looking to get more of:
Shares (of links to your site)
Mentions (in posts/in comments)
What's the current number of these you receive, or give out? Do you know how to measure that?
If you don't, check out circlecount.com, or allmyplus.com. Use the Social Reports in Google Analytics, or Google+ Ripples.
Once you know your stats, use them to build a simple set of goals.
"I want to get 100 new followers every week."
"I want to get a +1 for every post."
"I want five comments on my posts every day."
Then work out how to get there.
You might find, for example that responding to people who comment encourages more comments (or +1's), or that commenting on other people's posts gets you more followers.
At the end of the day though, it's only through taking action that you're going to reach those goals. You can read hundreds of articles telling you "how to succeed at social media", but it's the actions that count, right?