Just a quick note about making sure virtual keys and ads are placed where you expect in your GameMaker game. If you have something like this in a 960×540 resolution game:
virtual_key_add(0, 420, 256, 120, vk_left); virtual_key_add(704, 420, 256, 120, vk_right);
which places two virtual keys towards the bottom of the screen, then you’ll need to call display_set_gui_size(960,540) (or whatever your game’s resolution is) to ensure the keys are placed at the same relative position for devices with different resolutions. The same goes for placing ads on the screen.