Question: I have a log In page with username and password fields. I would like to know the best place to put the log-in button below them. Should it be left-aligned, centered, right-aligned or fill the entire width of the parent?

Is there a industry standard or best practice for Android Log In Buttons?

Answer: 
An idea would be to align them below the edit text views that will be completed. That's the most elegant way to do it.

You can try something like [this](http://info.ticketleap.com/Portals/117802/images/media/android-login.jpg) 

Or maybe something like [this one](http://farm3.static.flickr.com/2649/3925689032_c7f7151c33.jpg)
I would say put the login button below the fields. And center it, filling the same amount of space as the fields. This would look the best and would show up great in landscape and portrait.

A lot of companies put a lot of research into the best UI layouts.