If you get too caught up in trying to write for ranking systems, you'll end up with stuff that is either hard to read or something that just looks spammy--both of which will turn people off.  And, on top of that, the algos will eventually figure it out, while penalizing you in the process.

Check out these vids from SEOMoz.  I haven't had time to review them, but it seems like they should touch on what you are looking to understand.

I've seen the SEOMoz videos, but they largely confused me by talking about trying match Google's rankings without regard to keywords, which strike me as the most important part! I may get a page to rank highly for George Foreman grills but poorly on Weber grills, and not at all on car grills!

Thanks for the input. I figured the decrease was probably external to my actions, but that doesn't mean I don't want to work on increasing that score! I'll have to see about finding good ways to link to the homepage from some of my higher ranked pages and getting some guest posts done soon.

You could try linking to your homepage from interior pages (naturally, of course) or you could try doing guest posts or get mentioned in major new publications (which might include a link to your homepage).

ALSO, I would say that it's rare to see an active site's PA drop, so another thing to keep in mind is that the calculations that create the numerical score CHANGE. If it dropped unexpectedly, I would suspect that there was a drop across numerous sites, and not just yours.

That's my $.02.