Android Button Screen

Whats the best way to go about setting up a button anywhere on the android screen and have it versatile for any android phone screen size? Thank :)

Also Would:

var menu1 :Texture2D;

function OnGUI(){

 GUI.DrawTexture(Rect(0,0,Screen.width,Screen.height), menu1);

}

---Be a good Place to Start for my main Menu... The Whole Resolution conversion is throwing me off for the buttons and the background images for different types of phones and screen sizes.