To "burnish" means to rub something to a shine or gloss. It's not enough to slap some words down and hit the Send button! Take to heart the famous writing adage: "There is no great writing, there is only great re-writing." By the time you read these words, I will have tweaked them at least four times, checking for better and stronger ways to convey my message to you. I will double-triple checking for poor grammar or typos. After that, the editors at Entrepreneur.com will do it again - twice! Especially if English isn't your strong suit, write the first draft and then have it checked out by someone else. There's no shame in using an editor or editing yourself. Ideally, set your words aside for 24 hours and read them again before you send them off into the world.
It can help, but other degrees also have content writing value. For instance, the ability to synthesize and relate complex information is key to content writing, but can also be acquired from studies in education or philosophy. Companies that offer content writing positions tend to find it easier to train someone in a complex topic than to train someone to write, however. For example, as a healthcare professional with mediocre writing skills, you're less likely to be hired as a healthcare content writer than a strong writer with no healthcare background (but who can be trained in healthcare topics).