MSN is engine that is simple to manipulate with spammy page content, which makes its search results not as related as Google or Yahoo’s results. MSN gets it fair share of searches though so it is worth seo optimizing for.
SEO efforts for MSN won't be wasted if you have stong keyword density through Title, Description and Keyword Tags. Put main keywords close to start of title sentence. Ensure to use strong keyword rich internal navigation system, inter-linking all pages together. Using single keyword rich H1 tag and several H2’s will have a great effect with MSN.
MSN is strong on page theme’s so when optimizing for MSN, attempt to add important keywords through title tags across pages.
Optimizing for msn can certainly increase your presence on the web. Gaining top rankings on MSN is not much difficult if your site has fresh & original content that is being added regularly. Good optimization of your web pages can boost your rankings on MSN and other search engines. MSN has incorporated a new dimension in its algorithm and that is of "RankNet". This technique uses the patterns of search terms and then delivers the results on that pattern. You need not worry too much if you want to optimize for MSN.