I believe the briliance of the social media is the ability to post spontaneously. And like so much in life these days, the old rules aren't necessarily helpful when you are just jumping in. It's not that grammar or structure are no longer important, but rather, the idea that you have to polish your text or photoshop your your blemishes on your photos before posting is very old school.
Truth be told, social media is just life real life. Most people feel more comfortable with those who are willing to relax a bit and let their guard down when meeting others. I know this to be true -- my closest girlfriends are those whose homes aren't picked up each time I visit. (I can assure you, neither is mine!) And we all go out without makeup or our hair done -- and often meet for that first cup of coffee in our pjs. The truth is, we're ourselves no matter what the situation is. And in our real lives, sometimes, hell, most of the time, things are definitely NOT perfect. Showing up with your guard down goes very far in having genuine relationships.
It's great to have a clean house, and I love feeling polished -- but the point is that you don't have to be that way all the time and in fact, if you are, you can have the opposite effect on people than intended! Hard to believe, but its those flaws that make us who we are.
As for getting online -- I think the trick to posting is to share what you know and be open to differing opinions. And if you are going to post something controversial (anything political, religious or sexual in nature) then you should expect to attract people who are going to see it another way. That doesn't mean that you have to avoid this issues, but think before you post something that is absolute. Keeping the door open to discussion allows real conversations, real learning.
I think the worst thing is to allow your sense of perfection to ruin your opportunity to start whatever it is you have an urge to do or say. One of my favorite quotes ever? The one that I clipped out of a booklet when I was about 13 or 14 and have had with me (now tattered and torn) since then?
“Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it!”
― Johann Wolfgang von Goethe