This is all very game specific.
It all depends on how your game handles its UI and the size of things on screen to determine how you're going to solve the pixel density and resolution disparity issues (which should be pretty similar to how you're solving iPad vs iPhone, assuming you are).
Any optimizations you're doing for the iOS version should apply to the Android version. You really just need to get a couple of target devices and test on them.
As for specifics, if you're not using OpenGLES 2.0 and you are doing fixed function shader stuff you need to realize that you have fewer texture stages on Android hardware than on iOS hardware. It's generally 2 instead of 4 I think.
One thing that Android users are used to that you'll have to add is soft "back" button support. Basically check for
KeyCode.Escape and go "back" where appropriate. I think this also includes exiting the application if you're, for example, on the main menu.