I am only going to talk briefly about how I do it and why. I'm not going to address how to use these tools to the best of your ability because I'm not an expert and I'm always looking for more tips to maximize them. However, I've been blogging for over a year and a half and I have learned a lot, so today I'm sharing my knowledge with you.
Find me on Twitter
Facebook - I share my posts on my page twice a day. I schedule them so they're in between my Twitter shares. I'm also a member of several Facebook groups where I share my posts: Her Campus Blogger Network, Northeast Bloggers, Boston Bloggers, and BlogHer Network. Some of these groups only admit members of their larger network, like the Her Campus Blogger Network.
Find me on Facebook
Instagram - Honestly, I don't share my posts on Instagram very often. When I do, they're important ones or giveaway. I do this because I try to only post on Instagram twice a day at the max and I don't want my feed to be full of blog posts.
Find me on Instagram
Pinterest - However, I share them on Pinterest all the time. I try to do this during prime time (according to some, 1-4 PM and after 8 PM on weeknights is the best) and I share on multiple boards at different times to try and get the best exposure.
Find me on Pinterest
Google+ - I always submit my posts here once. Every now and then, a few weeks or months later, I'll submit it again to get more exposure.
Find me on Google+
Tumblr - I don't share every post on Tumblr, but I choose the ones that I think might be successful. The focus here is on the pictures, as Tumblr as a whole is more based on pictures than words, so I choose the best picture from a post and caption it with a sentence or more that will make people want to read it. I tag it with as many words or phrases that are relevant to increase the exposure, and I also add it to my queue so it will come up later. (I run my tumblr almost exclusively on a queue, posting 20 times a day over the course of 5 hours.)
Find me on Tumblr
Stumbleupon - Stumbleupon is a great way to reach people beyond your personal networks. But like every other network, you do need to share more than just your own posts. Whenever I add one of my posts, I like to spend a few minutes on the site stumbling and also add some other posts or pages from the Internet.
Find me on Stumblupon
How do your methods of sharing differ from mine?