You should always give a compliment in your comment or say something nice. Also be specific about your compliment don’t just say “it was awesome” say “I really liked how you explained why you had a space background and I thought it was really cool.”
Add Information
If you were on a blog that wrote something you researched like dogs, you could add new information by saying “did you know one of the smallest dog breeds is a Chihuahua.”
Make A Connection
Also if someone wrote a post about getting a pet and they said they felt very excited and nervous and when you got a pet you felt the same feelings you should add your connection in your comment.
Ask A Question
At the end of your quality comment you should ask a question. You should make your question related to their topic, if they wrote about soccer but you didn’t know the rules to soccer you could ask them how to play.
Proofread
After you write your comment make sure to reread it to check for spelling mistakes, punctuation and to see if it makes sense.