In my experience any epub will look good on ibooks automatically. The only place Apple rather obnoxiously ignores the spec is with font declarations on a variety of elements.
The latest version of iBooks does let you 'force' font declarations for everything, but you need to add a non-standard file, com.apple.ibooks.display-options.xml to the meta-inf folder.
Most of the other areas where Apple ignores the ePub spec is more along the lines of their own proprietary extensions to ePub, so you don't need to worry about those extensions with a 'standard' epub.
Best resource for iBooks tweaks is the Pigs and Gourds blog:
http://www.pigsgourdsandwikis.com/search/label/iBooks