How do I implement add rel=author for Google serps?

You’re spot on that the core of this nice new capability in Google search results (SERPs if you want to use the technical term) is the addition of a new attribute “rel=author” to your blog or Web articles, but it turns out that the situation is more complicated because you also need a Google Profile and you need to cross-link between your blog entries and Google Profile. And – yes, there’s a third step – you also need to link to an author information page on your own site too.
Lots to do for this to work and I’m guessing that there’ll be a lot of frustrated people who can’t quite figure out why they aren’t getting this to work, but if you take your time and go through all the steps I specify, you’ll get there. And if you’re in WordPress, I won’t be surprised if there’s a plug-in someone’ll write to ease at least that portion of the work.
There’s also another wrinkle because Google Profiles are migrating to the slick new Google Plus service, so I’ll talk about how to figure out which you should use and what you need from that too.
If you want to read Google’s instructions, by the way, here’s the link: Authorship. But I find it rather confusing so I dug around and found out some things through experimentation…
Getting Your Google Profile / Google Plus URL
To start, let’s look at the your Google Profile. It’s most easily accessed by going to profiles.google.com. In my case, it immediately pops over to my Google Plus account, and the resultant URL for that is:
    https://plus.google.com/110193533410016731852/posts
We want that URL, except we want to strip out the “/posts” suffix so it’s just a link to the top of my Plus account. If you have a Google Profile instead, you’ll see a very similar URL, just with a different subdomain. Again, strip it down so your numeric ID is the rightmost element of the URL.
For me, ultimately, the domain I’m going to use to point to my Google Plus profile is:
    https://plus.google.com/110193533410016731852
You can figure this out too. Just save it in an open tab and go to the next task, we’ll go back and use this information in a second.
Create an About Me page on your site
If you don’t already have an about the author or about me page on your site, you’ll need one, and it has to be on the same domain as the articles you want to tag. If you have a multi-author site then you might want to set up one of these for each author.
I actually had to set this up on AskDaveTaylor. I’ve run the site for years, but never added an “About Me” page. Now I have one: About Dave Taylor.
Link to your About Me page from your posts
This was the trickiest step for me because as a singe-author blog, I’ve never really had links to an about-me page. I didn’t need one! On the other hand, to get the rel=author stuff to work, it was time to add it. Since this blog is run on Movable Type it meant I needed to go into my individual entry template and add the following code:

The result you can see below this article, where there’s a link to my About page.
Your method of adding the author link might vary based on what blogging or content management tool you’re using, and if you have multiple authors, it’s a bit more complicated, but multi-author blogs are old news, so with a bit of creative searching you should be able to find what you need.
Link from your Author Page to your Google Profile
The next step is to copy that URL you figured out earlier from your Google Plus profile or Google Profile and make sure that there’s a link from your own author page to your Google profile. Mine looks like this:

Not too hard to add, but a critical step!
Last Step: Google Profile / Google Plus Profile back to your About Me page
This is the piece that closes the loop: you need to go to your Google Profile page or, if you have Google Plus already set up, that page, and add a link back to your About Me page on your own site. I’ll show the G+ approach, but they’re basically the same.
On your Google Plus page, click on the blue “Edit Profile” button and find the Links area on your profile:

Now click on it and you’ll be able to edit them and – more importantly – add a new one:

Looks good? Click on “Save” and you’re done.
Phew!
Testing what you’ve set up
You don’t have to just wonder whether you did it all correctly, though. You can use the Google Rich Snippet Testing Tool and see if everything’s set up properly.
The trick is to enter the URL of a blog page that has the new rel=author information on it, as I’ve done here:

Click on “Preview” and then look at the bottom, at “Extracted rich snippet data from the page”. You should see something like this:

The “search preview” doesn’t show an author page, but I think that it’s because they don’t want us getting too excited. If you see “Verified” in green, you’re done and you’ve got things set up properly. Nice job.
Now just wait and hopefully you’ll see your Google Plus / Google Profile image adjacent to your blog entries in the search engine in the very near future.