Many of us in the web marketing space have a love/hate relationship with the practice of leveraging blog comments as a marketing strategy. On the one hand, it can bring valuable participation and content to our sites and provide an outlet for us to reach other communities and bloggers/comment-enabled communities. But, it's also an endless source of spam and low quality contributions that teeter on the "publish-worthy" seesaw.

Given the ongoing popularity of this practice and some recent successes (and failures) I've observed and participated in personally in this arena, I felt it worthwhile to explore in more depth.

Why Comment on Blogs?

• Branding / Awareness - commenting on blogs will almost certainly get you at least a brief once-over from the writer, and consistent contributions are a proven way to build relationships with bloggers. That participation can also yield awareness and branding to the blog's audience, at least those who are consistent comment readers and interactors. Depending on the blog/sector and your goals, this can be a very positive marketing move.
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• Direct traffic - comments with links, especially those that are well-written and entice readers to click a link (rather than just being a random/irrelevant/spammy link drop) will send visits. If the post itself continues to earn traffic, this can even be an ongoing source of referrals to your site/page.
   
• SEO / Search Rankings - some blogs use "dofollow" links in the comments that are approved and may send search ranking value. However, it's generally my opinion that many of these links aren't treated as... let's say "impactfully" as normal links in the search engines' ranking systems. However, leaving a link that is so useful and valuable that the blog author edits his/her post to include it (something I've done many times here on SEOmoz and helped to make happen through my own comments) is definitely SEO accretive.
   
• Second-Order Marketing Impact - many of the effects you might feel from commenting aren't directly impactful, but instead come later on as a result of the post. e.g. the reporter who follows up on a comment for detail to include in a story, the link to your content that comes from another blog discussing your comment, etc.

Given these goals, it's essential to think a bit more strategically about the practice of commenting and participation. Whereas the right contribution can bring you all of the above, the wrong one(s) could adversely impact many of these.

10 Recommendations for Blog Comments

1. Read the last 5 posts made by the author - assuming you've never participated in this particular blog/community previously, make it a pre-requisite of commenting to read through their prior material. You'll get a good sense of the author, their interests, their perspective and their writing style. All of these will help you considerably to make a positive, impactful impression with your comment.
    
2. Read at least 3 posts worth of comments - If you don't read the comments on other posts, you may have a tough time getting a sense for the community's level and style of discourse, making your comment appear out of place. You want to stick out from the crowd, but not because you're an inexperienced contributor. If it's your first time to a site, don't just drive-by comment and link drop, take the time to understand protocol and your contribution will be far more likely to generate value.
    
3. Read previously posted comments on the thread - This one's obvious, but also oft-forgotten. In order to have a comment that the author and other readers will take seriously, you need to know what else was posted on the thread. If there's dozens or hundreds of comments, it's OK to skim, but make sure your point is being made and discussed earlier a reply or back-and-forth thread may even be a more appropriate place to post your content in these cases.
    
4. Write "more than a tweet and less than a blog post" - The exact amount is up to you, but generally speaking, the range between a long tweet (~140 characters) and 2-3 paragraphs (too short to be its own blog post) is ideal. It's easy to consume, but gives you enough room to make a substantive point (and potentially leave a relevant/useful link). If you do want to go much longer, write that post! The content will likely be more valuable for marketing on your site, and many times, the author may append their post to include your link. You can then make a short, relevant comment in the post itself and leave a link back to your more in-depth piece.
    
5. Never drop a pure bio/reference link - If you link with something like this, you're barking up the wrong tree:
   
   
   These sorts of "drive-by" link drops will get rejected 8/10 times and have the link removed before approval the rest. If you're going to leave a link, it better be highly relevant to the post, interesting to the audience and as non-promotional as possible (or, if it is highly promotional, prefaced transparently as such).
    
6. You may link to your own content a maximum of once in a comment - If you're linking to the content of others as a reference, it's fine to leave a link or two, even three (this can be particularly useful if you're referencing data points, studies, surveys, etc. that back up a point), but if it's promotional in any way (even if it simply exists on a site you own/control), best practice says keep it to one.
    
7. If at all possible, use your real identity and photo - The goodwill and trust built from an authentic human face and name that go together, match the bio/team of the site they link to and carry across mediums (Twitter, Facebook, etc.) is invaluable. It can often mean the difference between being treated as a respected new member vs. a black hat spammer. If at all possible, use your real identity, full name, and actual photo.
    
8. Be authentic and honest about who you are and why you're there - You may be paranoid that by admitting you're a marketer, a community manager, an SEO, etc. you'll be thought worse of and potentially excluded, but I can say from experience that honesty is the best policy and that being open about your motivations and background will more often than not build trust and acceptance. That said, in many communities, if your title is officially "SEO link builder" or "SEO specialist" you might want to modify that slightly to "organic marketing specialist" or "content marketer" or even "blogger," if the title fits. So long as those descriptions are still honest, they can lessen the negative perception that "SEO" unfortunately still carries.
    
9. It's OK to promote your comment (and their post) socially - Bloggers love getting their work tweeted/shared, so if you tweet/FB share a reference to your comment on their post, particularly if you call them out by name, it can have a very positive effect. For example:
   
   
    
10. Make your profile link point to an appropriate place - You can ruin a great comment by linking to what seems like a spammy/manipulative site. If you run a site that's completely off-topic for the blog/community to which you're contributing, at least point to your bio page on the site rather than the homepage. Seeing a great response from "Maggie Thompson" that links to "www.suffolkhomeloans.info" might get a link-strip, but linking to "www.suffolkhomeloans.info/maggies-bio.html" could very possibly pass the same smell test.

Looking forward to hearing your suggestions on comment marketing. And if you want to write your own blog post about it and link drop, feel free - the thumbs here at SEOmoz do a great job of sorting the great comments with links from the spammy, drive-by linkers.