Comments should be substantive and directly relate to the question/answer being discussed. Comments are not chat rooms.
Don't write a comment for the sake of gratitude (please vote instead). We know it's not very comfortable, but it helps reduce the amount of information noise, which is part of the objectives of our service. Give thanks in the form of helping others in the community (pass it on to someone else).
If you've used the solution – write down what happened in practice or give a link to a detailed report. This will be valuable to a wide circle of people, responsible and much better than a formal thank you.
Vote for comments that have been helpful to you.
Remove your comments that are no longer relevant. For example, when the author of the post added information at your request.
Comments that have been created as explanations for voting against a question/answer may express the voter's personal position, but this position should be expressed politely and be based on common sense and objective evaluation criteria.
Don't answer a question in the comments, that's what Answers is for.