usually I will prepare in site SEO first. after that try to build link and submit to some website directory.
There must be 3 reasons why you want to audit the seo of a site. 1) You hired a seo company and want to verify what they are doing. 2) You want to know what your competition is doing to overcome them 3) You are just another "forum seo guy" and don't even know where to start. Doesn't matter what your reason is, but to audit learn the basics of SEO. You will see all the information is public available. Good Luck.
You can try this one - www. stepforth.com/6-step-plan/web-site-audit/ and if you still confused about it, google will always there to give good information Just search buddy, goodluck!!