There are plenty of mistakes that bloggers make but don't think it's a big deal. In addition to this, mistakes don't have to be as drastic as they are made out to be. Mistakes can often be simple and sometimes be over looked. There are four mistakes that are made often and should be avoided.
Tags Not Used
I know for a fact that people don't like to use tags a lot so they avoid them altogether. Not using your tags means that you are missing out on potential traffic and potential ranking on the search engine. I know that you don't usually rank really high or get much exposure with tags, but it is still a good idea because eventually in the future it will be an X factor.
Write Enough Content
when writing a blog, you have to write enough content to even reach the attention of your audience and the search engines. Most people think of a blog as the same level as micro blogging. In other words, writing just enough to count as a post. This isn't going to bode well with your readers or with Google because the content may not be sufficient.
Not Pinging The Blog
Even though there really isn't anything much powerful about pinging your blog, it's useful in terms of alerting the search engines and the blog directories that you have updated your blog. It's not necessarily going to give you an "edge" in ranking high in the search engines. None the less, it can help you with search engine relevance if any.