Can anyone help me with SEO errors on my website please?

[Argyles]

Something I'd recommend to help you out is to use your keywords in your title. Keep in mind that every page should have a different title. Not a huge difference, but use different keywords that pertain to the content on that page.

I think you've done a good job, using the authorship meta is relatively new and I don't see enough people using this meta. Google loves to promote it's own products. Make sure you stay up on your +page and post on it.

Keep building quality links, submissions and you'll see more readers. Consider guest blogging or other sources that will help you.

The <h2> tag will be important to fix as it's part of your content. You can probably do this yourself.

Don't build for engines, build for your readers. Most sites are naturally indexed, so you've done a lot of on page. Work on building a site that makes your readers want to come back for fresh content.