Here are some tips on blog commenting for both bloggers and blog readers. Basically, if you're reading this, than it's for you, whether you write a blog or not :)

Tips for blog readers:
If you read something you like (here or on any other blog) let the author know! Comment, like the post on Facebook, etc. It really means a lot to bloggers. And I think it goes without saying that if you read something you don't like and feel a need to comment on it, just make sure you're respectful in your comment. Bloggers are people with feelings too! And FYI, I have awesome readers because none of the comments I've ever received have ever been anything but positive. :)
Check to see if you're a no-reply blogger and if you are, please fix it so I (and other bloggers) can respond to your comments!! Here's a great tutorial from Story of My Life on how to do that.
Tips for bloggers:
Reply to comments!!! There are some blogs I love reading and commenting on, but after dozens of comments and not a hint of a reply, I'll give up and stop commenting and sometimes even stop reading the blog because it feels like the blogger really doesn't care about his or her readers. Let your readers know that they matter. If you're not sure how to receive email notifications of comments, go to "settings" on your blog dashboard, then go to "Mobile and Email" and then fill out the "Comment Notification Email" box.
Comment on other blogs frequently. Not only is that simply a nice thing to do, but it also is a great way to build your blog readership and meet other bloggers. Make sure that you're not a no-reply blogger!
I have two words for you...word verification (also know as captcha). People are a lot less likely to comment on your blog if you require them to squint at a little box with nearly indecipherable letters and/or numbers and then translate that into another box. To disable this feature on your blog, go to "Settings," then "Posts and Comments." Where is says "Show word verification, click NO.
Make sure you read the comments for more tips and advice!
Do you have any tips to add?