Well, yes and no...
The decay and fall of guest blogging for SEO (mattcutts.com)
Matt Cutts works for Google and is sort of their mouthpiece for answering questions about SEO and what Google wants. He seems to be an interesting guy, too.
In this article, Matt talks about how guest blogging is kind of dead... at least the kind where you get articles from unknown people:
...someone sent me a spam email offering money to get links that pass PageRank. That’s a clear violation of Google’s quality guidelines. Moreover, we’ve been seeing more and more reports of “guest blogging” that are really “paying for PageRank” or worse, “we’ll insert some spammy links on your blog without you realizing it.”
Ultimately, this is why we can’t have nice things in the SEO space: a trend starts out as authentic. Then more and more people pile on until only the barest trace of legitimate behavior remains. We’ve reached the point in the downward spiral where people are hawking “guest post outsourcing” and writing articles about “how to automate guest blogging.”
So, back in the day, it was fine to do this but now it's been overused and spammed, so he does not suggest doing this.
My brother summarized Matt's article well:
"Essentially, if you write for another's blog, or have another blogger write for your blog, set a <nofollow> tag, in the HTML of the link back to the author's blog, in order to convey your intent to Google."
And then here's an article I wrote recently:
2014 SEO: Link Building (webstix.com)
In that article, I write about how forming relationships with other industry website owners is important. That still seems to be the way to go.
I've had a few websites that I own (like TheOriginalSource.com and EzineArticleHub.com) where I accept articles pretty much entirely from people I don't know (but, on the other hand, some that I've gotten to know). These sites have original content and some other requirements which makes them ok - not great but ok. Like I said, this type of link building used to work and these websites are not set up with any kind of misperception that the articles there are all from one person or something. They are set up to be article websites. Matt does reference Boing Boing in his post, which is along the same lines except they have staff writers.
Sites like I have are probably still ok or fine, like I said. The ones you want to make sure you have no links on are what are referred to as "Content Farms" which contain mainly spun or re-used content. Those are bad.
It may even be in your best interest to disavow links from websites that you've done article marketing with. In other words, it can be fixed and we can help if you want.
What you want to do is start commenting on industry related websites. Send a few emails to the authors and ask them genuine questions. Get to know them a bit and get some conversations going. After a while, you may get to know them well enough where you can ask them if they will let you guest post. Even then, make sure the link you get back to your website is a "no follow" link so that it doesn't look spammy. Don't worry, if your article is good and if that website gets good traffic, it'll pass traffic on to your website.
As always, the best kind of SEO (search engine optimization) is by writing great content on your own website. That's what Google seems to always like. You get credit for that content on your website and that content keeps working for you. I've said this a number of times here and it's still true.
Clients ask how long articles should be. I used to say 400-500 words or more but now the rule really is long enough to cover the points you're making and it should contain no fluff. So write enough to adequately cover the topic with good content and references. Don't add in anything extra as filler content to get your articles up to a certain word count.
What seems to also help is:
All of these are so that the article is easy to scan. In addition:
Basically, serve the searcher. Think about someone doing a search and finding your website. Answer their questions and help them. Give them useful information that you can back up with references. Make it useful with images and supporting videos.
If you're not sure what to write about, here's a good article I wrote:
More Ideas to Help You Write Content (webstix.com)
And then you always want to do good and thorough keyword research to make sure you're heading in the right direction.
Here's an addition: Google seemed to clarify what Cutts said:
Google Clarifies: Guest Blogging Is OK, But “Guest Blogging For SEO” Is Not (marketingland.com)