Well, most SEO audits are complete useless bullsh!t, to sell you service.
There are some automated websites that grade your site, but it is all just a load of sh!t.

Here are the most important things you need to know:
- Meta Title / Description optimized for keywords
- <h1> <h2> <h3> optimized for keywords
- no more than 2% keyword density
- use keywords first, last sentences
- Unique, relevant content on every page
- backlinks should point to proper page and anchor text should be keywords
- you need twitter, facebook and google plus buttons on your site.
- you need to find a way to get real people to click the social buttons on your site
- use nofollow fo external links
- make sure you have good backlink diversity (gov,edu,related niches, etc)

If you use wordpress, it makes it easy, they have plugins for SEO...

I agree with friedman , most of those are worthless , however if you wanna do it you may try seo power suite , it will tell u something like the keyword xyz is too much in H1 tag and it is few in title .... etc ..but in my opinion off-page SEO ( backlinks ) is more important than on-page SEO

Great post Friedman. I would recommend just using a free service, there are many online that you can find with a quick Google search.

Here's one: Website SEO Tool | Website Grader