Juliana Smith recently posted my article "Getting the Most out of Obituaties" newspapers on the Ancestry.com site.
Some of the suggestions are general for searching any newspaper, online or not. Some suggestions are based upon the fact that the searches of Ancestry's papers are done with OCR technology.
I've spent some time searching the several Davenport, Iowa, newspapers on their site. The obituary for a Conrad Krebs is used as an illustration in the article.
The article can be viewed on Ancestry's blog here.