What are best practices for guest posting? Should it be a unique/new post? Or can a previously written/published post be shared onto another site? Anything else I should be aware of ?
The key to writing a high-quality guest blog is to think of it as a value-add for your audience — not merely as an advertisement!
Paraphrasing is the best answer here. If you write a whole new article, it may seem irrelevant to link it back to the original article on your blog/website.
However, if you borrow the main points from your article and elaborate on them on the guest blog, linking it back may seem more logical to google and readers as well.
Are you guest posting on someone else’s site? Have they given you any guidelines for what they want?
If you use something already written - and why not, you’d still want to update it, be sure it’s geared towards the new audience and give them a little love! Always have a shout out and call to action for them.
My understanding is that you don’t want to duplicate an existing post, unless you are very specifically aiming to do it as a “syndicated post” that clearly gives your site credit as the original source. Otherwise they posts would compete with one another for the same keywords.
It’s a fairly technical thing to properly have a post syndicated. I sometimes have wineries that want to feature my recipes. It’s been a struggle to get them to agree to and properly implement syndication.
To make high quality SEO optimization, you should write good individual content.