different screen sizes and camera

i want my game run in all screen sizes.and my question is simple.should i re size every element in the game or just move the camera back and forth or do both of them?
2.the ongui plugin is faster to re size and better or just attach a script to every element to re size depends on screen size?and do you have a script to let me know how should i do this?
thanks.

Unity should automatically resize everything with screen sizes and their resolutions. Build a standalone version of your scene, run it in windowed mode and then resize the window to see how things in your scene react