Attention to detail is a trait sought after in all freelancers, and it is something your niche article is missing.
In addition to grammatical corrections, it requires pull elements to draw the reader in - my idea is to include some statistics demonstrating the long-term benefits guitar playing has on mental health, or other compelling arguments.
I would also recommend including some hyperlinks to online tutorials, and online printouts for those interested in learning to play the guitar while at home.
Finally, this first article needs to demonstrate a larger connection to the website's mission, or at least other content posted. To this end, I would read a few other articles, and increase readership of past content by incorporating similar pieces throughout, or towards the end of, the corrected piece(s).
Thanks for taking the time to read this, and I hope to be able to work with you.
Sincerely,
Gabriela Taveras