After on-page is perfect, then what?

[webtarget]

I am working on a friend's site and I've optimized his on-page stuff. It's pretty much perfect from SEOMoz analysis. I reduced his Errors from 150+ to 3 and his warnings from 50+ to 0. Notices are at 5.

Now, a month has gone by and I've added 3 backlinks in what appears to be reputable sites PR7, PR7, and PR3. His site has dropped  from the 2nd listing on the 2nd page to the bottom of the 2nd page now.

Now, I realize other sites may be doing seo as well and trying to move to the top, but, seems peculiar. I put in a bit of work to revamp 3 of his pages as well b/c each one had over 300 html validation errors and I reduced it down to 6 or so.

The competitor I'm aiming for has these stats:

DA: 16

MozRank 3.14

MozTrust: 2.73

My friend's site is:

DA: 19

MozRank: 2.21

MozTrust: 2.64

Subdomain metrics is 0 for everything, whereas his competitors have good stats for subdomain metrics. What is that?

And what can I do to improve his ranking in Google? Is it just more backlinks?

Thanks.

[webfeatseo]

Are you able to share the url? What links you got? How you got them and etc?

[EGOL]

The deeper you go into the rankings the more flux you will see - because all of the shuffle above and below can jostle you around.

Also, for sites with a DA in the teens you should expect more shuffle than those with a lot higher DA.

To close... for the past few weeks I have been seeing more than normal flux in most of the product SERPs that I am watching.

The moves that you describe are not surprising, I would say they are common.