First of all you should have a good theme, that will force people to leave comments, either to agree or not with you.
Second, the post should not be overly long, because people do not like to read. Post should be short and clear. You do not need to write too much about the details, you should tell only the essence, because that is what people are interested. Write only the most important things: what, how and where. Give people basic information, and they will leave a comment, and you'll get more comments, more Google will value your blog.
I noticed that people prefer posts written bold letters, probably because these posts are easier to read, because less tauten eyes. On the other hand people do not like italic letters, and avoid using them, unless emphasize some keywords, and make sure to change the color of the word.
Do not write all in one section, create posts so that the space between the paragraphs to be one row. One of the reasons is that it looks nice and steady, and the other because it gives people the feeling that the text is not so long, this means to have less to read, and the third reason is that transcends the lines because people often lose in such texts, so the best is to text divided into smaller units that are extracted from the text.
To all this, and you will have a post that people will love to read and leave comments.