Using proper grammar and pronunciation are a massive contributor as to how you're viewed virtually. Use facts and speak to others with respect. Don't be a drag, try and stay optimistic and cheerful.
Depends what your goal of using the social media account is for. If it's something like LinkedIn, keep it strictly professional or related to your work.
I have a couple of personal accounts on Twitter and Facebook, but they're all on private.
Have two accounts. One that's actually going to be a presentable you, and the other for chatting with friends and anything people might consider objectionable like NSFW... that's how I do it...
I use Twitter for my forum. I don't behave irresponsibly on there because that's what I use to promote my forum and I don't want someone to get turned off by bad behavior and not want to join my forum.
My take on social media is a connection with the people you like. The behavior need not be professional but just decent and somewhat honest. I have 833 friends now with just about half of them active. From time to time I unfriend some of the inactive to reach my goal of 500 friends only. With that number I can react to all the posts even if not all of the time.