How to create a unique looking inspector,

How do I make a GUISkin or GUIStyle override Unitys default inspector so that my scripts look unique and are easier to organise visually (In the inspector)?

I'm aware that it involves Using an editor script and

@CustomEditor(NPC001)

class MyPlayerEditor extends Editor {

function OnInspectorGUI() {

//stuff goes here

    }

}

But I cant seem to apply the GUISkin or style to the script in the inspector., to change its appearance.

TIA AC