Titles: Keep your title tag short (around 5 words) mentioning
your target key phrase no more than once. No different than
Google here, except by the amount of words.

Descriptions: 15 " 18 words total including your target key
phrase at the beginning, keeping the overall text very
descriptive. You should include an alternative version of your
key phrase as well if possible.

Keywords: Unlike Google, Yahoo still uses this tag as part of
their ranking evaluation process. Including the most relevant
words to the content of the page at front, make sure
additional words are still found within your content for
maximum benefit. Keep your tag up to 200 characters in length
" without commas. No, they would not look like one word
altogether, and this is part of the indexing process anyways,
were commas get removed. You can keep a comma delimited
version for own SEO tracking.

Headings: H1 and H2 should be used containing the key phrases
and to keep the on-topic relevancy of your content.

Topical and Navigational Links: When applicable, use links to
other sites that further re-enforce the topical nature of your
content. That is the basis of what all search engines perceive
as relevant, quality links. These are basically one way links
from sites that specialize in content directly relevant to the
content on your own website. In terms of navigation, you
should link internal pages from a broad topic, to a narrower
topic, to a specific topic.

Keywords in URL: Even they don't carry a lot of weight with
Yahoo, topical keyword-based filenames can give you additional
boost over your competitors, so they should be implemented.