Just in case anybody's new to the series, or simply needs a refresher, IGN has a really helpful guide. Although most of it is DOA2U specific, it does have some stuff that is universal to all DOA games. It covers the system, advanced strategy, and important moves/simple combos for all characters.
http://guides.ign.com/guides/566556/page_5.html
http://guides.ign.com/guides/566556/page_5.html