Many beginner bloggers think that more is better and actually I am here to tell you that actually less is better.
From my experience as a professional blogger, the best length for a blog post is about 250 to 350 words. This is enough content to really flesh out one idea and yet small enough to not bore your readers. On top of that, it is easier to build strong keyword density on one topic in a shorter blog post then it is to build density in a long blog post.
For my professional writers I recommend that they write their blog post in the blog control panel and then migrate it to Word to do a quick word count, until they get a good feeling about how long a post is. The more you blog the better you get at gaging just how many words are in a typical post.
Another thing to remember is that content scanning is a typical behavior on the Web. So paragraphs that will be published on the Web should be shorter versus those in print publications. A typical web content paragraph will be about two or three sentences long versus a print version being more like five to six sentences long.
Studies have been done on Web content that show if the paragraph is too long, a reader may skip it entirely. So, when writing for the Web on blogs, remember shorter is better both for post length as well as for paragraph length.
Just as a point of reference, the blog post above is 251 words.