Android : Support multiple screen size and density in android

I am trying to design an android app which has some buttons organized in rows and columns and I am using LinearLayout to organize my content. To be able to support different screen sizes I am using layout, layout-small, layout-large, layout-xlarge folders to contain my layouts. But my UI does not work on different screen density. How can I make my UI support all different screen sizes/density? I am using emulators to view my UI. Also emulator does not pick up landscape UI automatically while the same work on actual device.

Thanks