Did you submitted the xml site map to Bing Webmaster Tools? Please also create the meta tags for Bing & Yahoo crawlers.
We have the same experience with those SE's.. I know its very great to have a good ranking on those 3 search engines.. but for the meantime, I will focus ranking my keywords first on Google before ranking on Bing and Yahoo.
Doing same activities for all of search engine. Write metag according to search engine and promote it.
make sure your site is indexing by yahoo, but if you are at high rank on google soon you reach on the high rank on yahoo and bing also, because ranking on google effect on other search engine also.
Many times when your websites gets ranked well on the Google then after some weeks your website will be indexed and ranked on the Yahoo and Bing so keep good working.
I came across this page in the Bing Community forums. There's a list there of links to pages that give information on how you can improve your rank in Bing. Hope that helps. Have a good day!