First, you want to ask yourself why do you want to leave that comment and what do you want your comment to accomplish? Thinking about this will put you in the right frame of mind for leaving a proper comment.
#2 Be Respectful and Courteous even if you disagree with the person, be polite and kind with your comments.
#3 Don’t Comment just to have a Backlink. Having a link in the comment is a big way to get marked as spam so don’t try to comment just to get a backlink.
#4 Add Value to the Discussion. Have you ever looked through comments and just saw I agree or nice post? These aren’t really adding value to the discussion, instead if you do agree, add why and what parts of the post you agree with.
#5 Spellcheck and Proofread. Grammar goes a long way in getting approved and making sure you don’t have all caps on is a plus.
#6 Retweet, Share, and Reblog. If you think a post is worthy enough for your comment, you might want to consider sharing it with your audience as well.
And #7 is Private Feedback. You want to keep the comments about the post or article. But if you have something else to discuss with the author or a suggestion for them, then use the contact form or their email instead.