Tell your friends to do it for you. You know,those who follow you on twitter, facebook fans etc. You can set up a system whereby your friends will be redirected anonymously to the page which you're ranked on a specific keyword.
The best way is to provide quality unique information on your site... and you will get more pluses than you can buy
The safest way is to ask for +1 for your friends and everyone you know personally. Other things like buying, exchanging, making them via fake profiles can really harm your website. Of course there are not bad cases so far, but I believe that Google will do something about it
I have try tweer to get get exchange google plus and I got 10g+ for first day but next day google removed them all.
You just need to get the word spread around the web. Tell all of your friends about your stuff and then promote the page you want ranked for a specific keyword.
How do you get Facebook likes? It's pretty much the same idea. Work on more mainstream ideas and content that the majority of people will like and you'll probably get more than your usual share.
I would think unique quality content. Plus build backlinks forums and blogs are a good way to do that. Also create a facebook fan page its no follow but powerful like other sites related to yours. also on forum and blog comments make sure they are do follow which most are now a days and related to your niche if possiable.