Hi there Ed,
SEO is a huge subject - loads of different pet theories from loads of different experts. I've seen articles saying that the importance of h1 tag is overrated, but most seem to agree that it is one of the main criteria in getting yourself seen. The people here say, "Significance of h1 tags has multiplied in recent years. Google’s search engine crawler gives more importance to h1 tags than keyword and description meta tags."
The general concensus seems to be to make every word count not just in the meta tags but in all the main hot-spots, i.e. between the page <title> tags, the heading tags, and the menu stucture item descriptions. Most 'Home' pages carry a first-paragraph mission-statement type introduction to the site's business, which generally remains the same, so the home page is important. Each page should deliver what it's meta tags promises. As to what your clients might put into the content areas, there's not much you can do to influence that.
A well defined and relevent (current) html site-map along with regularly submitted site-map xml is important - there are many solutions for this, - have a look at WebAssist's Surveyor. It all adds up.
It's good that you're thinking about it now, though - it is often an afterthought for a designer.
I probably know less about this that most, so it would worth puting in the time doing a round of the forums asking for tips, just to get an idea of the current concensus and memes.