It really depends on the particular app, existing UX, branding and a ton of other design considerations.
In general, starting from scratch, a good starting point (though not universally!) would be the action bar. It gives the user access to ways of manipulating the data on screen, as well as a way of consistently presenting secondary functionality (the overflow menu). Design docs, implementation docs.
I would heartily recommend going through the Patterns section of the design documentation, as it explains the rationale behind many of the core design decisions.
P.S. The reason I'm eager to underline that it's not universal is apps with established UX and user expectations. Examples include Facebook, Path, Google Maps. They all have their reasons for not sticking strictly to the action bar paradigms but they work with it as much as they can.