Just like people, search engines have their likes and dislikes too. Knowing this fact, you should do everything you can to appease the search engines.
Keyword Use in Title Tag
The absolutely effective 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 conflicting title tags since each page that reflect the content of that particular page - otherwise, you may thrill from a duplicative content exclusion and obtain yourself in the supplemental results).
Keyword Use in Body Text
Duh. If your keyword or keyphrase isn't make reference toed at least once in the body text of the web page, then it does not seem your page is very suitable to that keyphrase, now does it? But don't get all caught up in the keyphrase density myth - there is no magic number of times it should be present at. Transform sense to readers, and it will appoint value to the search engines.
Relationship of Body Text Content to Keywords (Topic Analysis)
Google is smarter than you give them credit so that, and just stuffing a keyphrase into a completely unrelated page won't do you a great deal, if any respected. 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 so that thinking otherwise. Considerably the verdict is in and this is the fourth almost dominant factor according to the SEOMoz article. At this point, therefore, we have self-instructed to put your key phrase in your title tag, include 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 disagree with. I have seen totally no indication of this at all. Do a simple search on the internet so that most any search term, and chances are the top results do not have the search query in the domain name. I presume this may have minor importance, but don't go and change your domain because of it. Seriously, you have a great deal more to lose (such as age of domain, inbound linkage, site reputation, etc.) I regularly discover clients at the top of Google with domain names containing nothing near the relevant search terms.
Keyword Use in Page URL
This is what I have called "descriptive file naming" since a number of years. I think it is of some importance, again, however, is more of a thing when setting up a new domain than would be for an existing domain with high pagerank and inbound linkage. Changing your internal url's so that the sole purpose of meeting this criterion again is very risky, for the same reasons bring to attentioned above.
Keyword Use in H2, H3, H... Tags
Correctly if it works for H1, why not for 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 laterally, I suppose this to be a great deal powerful, I would have ranked this above the URL and domain name content. Experience has shown me that image optimization (image file name, alt attribute, and title) is a wonderful way to transform a page more suitable to a desired search query.
Keyword Use in Bold - Strong Tags
I always use this algorithm, as effectively as keyword use within the EM (italics) tag. I suspect this to be a moderately meaningful basis as it helps underscore to Google what your page is about, and what you consider valuable. Rigorously on my short list of things to do for "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 mention body text in my big four as I suspect that is self evident. Rigorously authoritative, and again, each page should have custom title and meta description tags.