Always consider the background color against the color of the actual button. It is not recommended to put the solid blue button on a blue background. It is also not recommended to put the gradient button on a similar blue/green background. When possible, it is recommended to use the light and dark versions of the button for simplicity sake.
Clear Space and Padding
Always maintain the minimum amount of clear space around the logo if needed.
You can scale the button as needed for different devices and screen sizes, but you must preserve the aspect ratio.