Keyword Use in Title Tag
The most authoritative post to put your Keywords into. Put your keyphrases in your title tag, and remember to optimize each page individually (Ex.. don't overstuff your title tag, and have unequal title tags since each page that reflect the content of that particular page - otherwise, you may thrill from a duplicative content exclusion and locating yourself in the supplemental results).
Keyword Use in Body Text
Duh. If your keyword or keyphrase isn't bring to attentioned at least once in the body text of the web page, then it does not seem your page is very significant to that keyphrase, now does it? But don't return all caught up in the keyphrase density myth - there is no magic number of times it should be present at. Produce sense to readers, and it will shape value to the search engines.
Relationship of Body Text Content to Keywords (Topic Analysis)
Google is smarter than you give them credit for, and just stuffing a keyphrase into a completely unrelated page won't do you a lot, if any delightful. Your page should be on a topic which is semantically related to the keyphrase which you are targeting in your title tag.
Keyword Use in H1 Tag
Oh, for years the naysayers have been telling me that H1 tag keyphrase use meant nothing and that I was an idiot since thinking otherwise. Deep the verdict is in and this is the fourth most worthy ingredient according to the SEOMoz article. At this point, therefore, we have learned to put your key phrase in your title tag, embrace it in your body text, which body text is topically or semantically related to the keyphrase, and head up the body text with an H1 containing the keyphrase.
Keyword Use in Domain Name
This is one that I hold out against with. I have seen actually no clue of this at all. Do a simple search on the internet for absolutely any search term, and chances are the top results do not have the search query in the domain name. I suspect this may have minor significance, but don't go and change your domain cause of it. Seriously, you have a lot more to lose (such as age of domain, inbound linkage, site reputation, etc.) I regularly notice clients at the top of Google with domain names containing nothing near the suited search terms.
Keyword Use in Page URL
This is what I have called "descriptive file naming" for a number of years. I think it is of some importance, again, however, is more of a point when setting up a new domain than would be so that an existing domain with high pagerank and inbound linkage. Changing your internal url's for the sole purpose of meeting this criterion again is very risky, for the same reasons make reference toed above.
Keyword Use in H2, H3, H... Tags
Well if it works since H1, why not since H2, H3, H4, H5 ?
Keyword Use in ALT Attributes and Image Titles
SEOMoz incorrectly calls them an ALT tag, but it is not a tag, the ALT is an attribute of the IMG tag. Semantics in an aside, I have confidence in this to be powerfully authoritative, I would have ranked this above the URL and domain name index. Experience has shown me that image optimization (image file name, alt attribute, and title) is a remarkable way to manage a page more suitable to a desired search query.
Keyword Use in Bold - Strong Tags
I always use this strategy, as effectively as keyword use within the EM (italics) tag. I believe this to be a moderately valuable aspect as it helps pinpoint to Google what your page is about, and what you consider effective. Definitely on my short list of things to do since "on page" search engine optimization.
Keyword Use in Meta Description Tag
Again, one of my "big four" for on page optimization. The "big 4" being: title tag, meta description, H1, and image ALT attributes. I don't bring to attention body text in my big four as I believe that is self evident. Indeed superior, and again, each page should have custom title and meta description tags.
James Saunders is the owner of http://TrafficBoosterPro.com, the SEO software which makes Unique Content pages Quickly and Easily! Software that bring massive Traffic from RSS Feeds in AutoPilot, now in it's 2nd revision at http://TrafficBoosterProV2.com