TL;DR My bottom line suggestion is to first start with blogs (get a feed reader and subscribe, read and comment on blogs). Next join Reddit and subscribe to the sub-reddits you are interested in, and participate. Next start your own blog. Then join Twitter, LinkedIn, Google+. Put your learning first; other measures are largely “fools gold” (such as number of followers).
Blogs are the best way to use the internet to learn, network, share and grow. That includes reading blogs, commenting on blogs and writing your own blog. Thankfully there are tons of great management improvement blogs (especially on lean thinking) for managers to learn from. There is a great opportunity for six sigma blogs as the field is not crowded with high value blogs on that topic.
Writing your own blog is the very best online way to create a brand for yourself (and to learn and grow). Given the workplace today, and how the future seems likely to unfold, building your own brand is a valuable career tool. Writing your own blog also builds your understanding of the topic. As you put your thoughts into words you have to examine them and often build a more complete understanding yourself before you can write about it.
You also build a network as you read and comment on other’s blogs and as others read and comment on your blog. YouTube can be used in a similar way (though I would use a blog to add text to the webcast and encourage comments on the blog rather than YouTube). Using an RSS blog feed reader is the first social network tool you should use (way before you sign up for Twitter or Facebook or anything). Podcasts can also. I have done a few podcast, most discussing the ideas in my management book. Videos and audio connect more deeply to people so they are wonderful methods to reach people. I should get some webcast up on YouTube; it is one of my plans that I haven’t gotten to you yet.