Just start and I believe you will get better with time. Right now writing probably frightens you, but that will pass. You're going to do just fine!

That fact that you just wrote about it says something of your character. The only way you can fail is to quit.

Everyone gets writers block. Everyone fumbles through their posts sometimes. When I experience this, here is what I do: Write a blog post in the morning about something... anything. It does not even need to be about your niche. Save the draft and walk away from it. Go and read some other blogs or pages relevant to your niche and give them constructive criticism in a comment. After a few hours go back to your blog post and thoroughly read it. Fix the stuff you want to fix and post it or toss it and start a new one. You may find that you got some inspiration in your other reading.

Just remember the key is content. When you first start writing your content is not going to be filled with as much quality as it is after you've been doing it for a while.

I find that reading A LOT helps people be better writers. What you read is not relevant so read what you enjoy reading.

Good luck. Keep it up and don't quit!