Keeping a check on how the final product looks shows that you are more serious about blogging. And, good language is very very essential. Otherwise, it can be a huge turnoff for people. No one likes excessive grammatical or spelling mistakes. One or two per post is forgivable but if it keeps on occurring in every paragraph, while focus of the reader goes to the next mistake instead of what you are trying to convey.
Also, one of the key tips while writing is to be as precise and short as possible. Try to keep the posts short to 300 to 500 words and wrap up everything in that. If it goes beyond that, turn it into another post. Keep the language simple and easy to understand.
And, keep using the preview option till you are satisfied with the final look of your post. Yes, it takes time but it is satisfying when you see the results! Also, when you reread your post, the ideas start flowing and the shape of your entire post changes as it did with me for this particular post!!
Do you read your posts again and again till you are satisfied with it?
Related Posts: Blogger Series Vol. 7 - Should you give feedback to your blogger? Blogging Series Vol. 6 - How to design the layout of the blog? Blogging Series Vol. 5 - How to time the posts?