Actually, these are issues I see in all writing, online and offline.
1. Delete the word 'very' from your vocabulary. If you're happy, be happy - show the reader what you mean, don't fall back on a support word like "very". If you're mad - well, don't be mad; if you think you can be 'very' mad - think again. Might lead folks to call 911.
2. Maintain tenses. If you're writing in present tense, stay there. "I was off to the dog park and when we got there..." is just plain wrong. It's either, "We were off to the dog park and when we got there..." Or, "I was off to the dog park and when I got there..."
3. Recognize editorial content and opinion - don't present your opinion as fact. Blogs are notorious about this. Yes, as a blogger, you are right to voice opinion and be personal. Use "I" often. But, if you're "reporting" - cite your facts (three are usually good but add more if you have them), and note where your personal opinion begins and stops.
"I just read the latest NYTimes <link> article about how dogs think <link to another source> and had some thoughts on it. First of all, how can any intelligent person not believe dogs think? The articles online support belief that our furry friends do think <link to scientific study> and I, personally, have always believed it."
4. Don't quote others without context and supporting information. Seriously, in your blog always provide a permalink. In your print writing, show the location of your source.
5. Learn how to spell. No, really...learn how to spell. It's "definitely" not "definately"... and, "you're" not "your" if you mean you are, and "their" for possesive, "there" for location, "they're" for they are. And for goodness sake, it's "it's" for it is and "its" for possesive!!!
6. Own up to your mistakes. I make grammar mistakes, typos and even forget to cite sources, once in a while. I don't profess to be perfect. When I make a mistake and someone calls me on it, I own up. I don't make excuses. Truth is - if you want to be taken seriously, you do what you can NOT to make mistakes but when they happen, it's mea culpa. Using style guides helps.
7. Links that don't work. I understand that links break. And, honestly, older posts may have broken links because the linked page no longer exists. However, within your blog, your links need to work. If I click your "about" link, it better take me to an about page. If I click your contact me link, it better show me a way to contact you. Don't send me to your resume page. Don't send me to another blog you write. Don't send me all around the web. Don't hinder me in finding what I'm looking for on your blog.
8. Not telling me who you are. OMG! I don't want a third person account: "Peggy graduated Summa Cum Laude from a high powered university and worked at Rodgers Publishing for six years. She left Rodgers to become a consultant..." Really? That's what you're offering me about YOU?
How about, "I love pets. I've loved pets my entire life - even while studying finance at my local Community College. My background is in publishing and that's one of the reasons I started this pet blog. I have a bull terrier and a fluffy mixed-breed cat and I lust after Golden-Doodles, but don't hold that against me!" Ah, now I'm feeling like I know you.
9. Long, dense paragraphs turn me off! Reading on a computer monitor causes eye strain. Trying to read long, dense paragraphs gives most people pause. Your message should be succinct and to the point, and any added material offered in short, bulleted points or one or two sentence paragraphs. Helps folks who read your stuff on a cell phone, too.
10. Not including images with your blog post! In the early days of the blogosphere, images were vital. People knew readers needed that break in text - an image worth a thousand words - to help them appreciate the blog message. Sometimes, the image can be the attention grabber. Without it, your post is just a lot of text, text, text...that I have to wade through. Give me a break! Show me a picture!
I'm sure you have your own pet peeves. Share'em with our readers. What have I done lately to annoy you? I can take it...tell me ...