I have been editing at Bioethics Today for 2 years.
These are the 3 simple (but effective) pieces of advice I'd give anyone starting out (or who wants to get started) writing opinion essays:
Advice #1: Make ONE CLEAR point
Many new writers get so excited to write about a topic that they end up writing about 4 or 5 topics without even realizing it. The reader gets lost trying to figure out your point. Don't leave readers guessing! Choose one point you want to discuss and stay focused.
Advice #2: Write as simply as possible
Keep readers engaged by writing in straightforward and easy-to-understand sentences. No run-on sentences. No flowery language. If it's too complicated, your reader moves on.
Advice #3: Own your point of view
To have an opinion, you must bring your point of view. What unique perspective do you bring to your specific topic? Why should the reader care what you think? Tell them why!
Honestly, I wish someone had told me these 3 things earlier in my writing career.
But I'm at least glad I can pass them along to you.