Need some tips for blog commenting

Jonathan is right on this. (ASIDE: note I've now mentioned Jonathan's comment and made it clear I read it because the rest of my post alludes to it.)

From the blog owner's perspective comments are to extend and expand on the conversation started by the post, not for you to toss off a few words so you can drop a link.

They only care about your links at all if it is going to another piece of content that adds value to what their readers have found on the post and are discussing. They want people to come by and add their thoughts on the post, feedback about it, etc.

The key is adding real value. Ask yourself - did I contribute something that expanded on the topic, asked for help if something in the post confused me, or offered additional useful content sources for others to check out? That's what a GOOD comment is. You are offering value, you are moving the conversation forward, and you are rewarded with a reasonable link in the website box.

They really want others to "join" the conversation by talking about the post, talking about what others have said that you find interesting or helpful, or asking clarifying questions.

In other words, a conversation between multiple parties, of which you are one.

(Rant, sorry). Way too many comments are trivial, have no intention of providing useful content that adds to the information present, and throw out links that don't help the conversation along.
(end)

Comments don't have to be long (mine are because I have an inevitable tendency to long-windedness and detailed explanations. Too techie, I guess.

You are entitled to a link and it doesn't HAVE to be relevant, but only if you earn it. And don't dump keyword anchor text in there to a site that obviously exists just sell something to someone unrelated to the blog topic. That belongs in the website box as your allowed reward of self promotion (if your comment is worth approving). Most bloggers will kill comments that are full of useless links in the body text. That's reserved for helpful links.

So, if you just skimmed the middle here:
1. Add real value. It can be short if it is informative. No "me too."
2. Only offer clarification or information links if it helps out the post and comments of others.
3. For best results, join the full conversation that is occurring between blogger and his audience. Then you are part of the audience and not an intruder. And if you become a regular commenter with value, you've got a relationship you can build on.

This is something that I do frequently and it really, really helps.

Thats a smart way of blog commenting.
We all know that MODERATED and relevant blogs give quality backlinks and help build your brand in your niche,so the best thing is to post only readable,though provoking comments that share insight on the subject.

Jonathan is right about responding to or adding to other comments. It's effective. Although, I'm not an advocate of "instead of reading the article." To me, a quality backlink is well worth the time to read that article. Especially since that blog article "should be" related to your niche. It's a great opportunity to further educate yourself on that topic so you can speak more eloquently in the future when you comment on those niche-related articles. Good luck.

Search theme related blogs, read the blog and reply from others and then write your reply about this topic. Do not spamming on it.