Below is a summary/excerpts of a great post by Pro Blog Design. Read their entire article here for lots of great code and specifics.
“Comments are gold. … It’s great to know people want to engage with you, and they can add a lot to an article. However, if comments are not done well, they can be difficult to read and follow, or even just downright boring.
What we’re going to do first is create a custom comment callback that allows us to specify the way the comments are output, then lay out the structure for the comment list and reply form, add extra functionality such as author-only styles, implement comment subscription options and spam protection, and, finally, we’ll add nice CSS styling to everything we’ve done.”
(They work with the default WordPress theme in order to make everything easy to follow)
1 – Create Custom Comment Callback
The comment callback is just a way of telling WordPress what HTML to spit out for your comments.
2 – Lay Out Your Template File
The code in the previous section created the structure for individual comments, now we need to lay out the structure for the actual comments page, on which all of the comments will be displayed (Including the comment form).
3 – Enable Nested Comments
People have mixed feelings about threaded comments, but they can be quite useful in organizing the discussion flow. This step is entirely optional…
4 – Make the Author Stand Out
Particularly useful for people who write tutorials and need to answer questions from their readers, this bit of code will make any comment left by the author of the article stand out from the community’s comments.
5 – Disable Comments on Old Posts
6 – Subscribe to Comments
Often times a reader will ask a support question via post comments. Receiving an email whenever another comment is posted is a much easier way for that reader to know an answer has been posted than manually checking every now and then (if they even remember to do that).
Subscribe to Comments by Mark Jaquith is a great plugin that adds a link to subscribe to further comments just below the message box of the comments page. It also includes a subscription manager that is placed under Tools in your WordPress Dashboard, allowing users to unsubscribe from posts at any time.
7 – Add Extra Moderation Links
Even with anti-spam protection, you will occasionally have comments that you need to mark as spam or delete entirely
8 – Add an Extra Layer of Spam Protection
9 – Add Comment Feed Link
10 – Display Allowed (HTML) Tags
11 – Show Total Number of Comments
12 – Add Some CSS
Again, this is just a quick overview of a great post on Pro Blog Design. Read their entire article here.