How to effectivly use the CFrame rotation?

The parameter to CFrame.new(pos) is a position, which is a Vector3, not a CFrame. Use

either

CFrame.new( script.Parent.CFrame.p )

or

CFrame.new( script.Parent.Position )

You probably want to rotate by less than 1. CFrame.Angles parameters, unlike the Rotation property, is measured in radians not degrees. Though it's probably better that you just keep track of the angle rather than read the property as you are doing:

local angle = 0

while wait() do
	angle = angle + 0.1
	script.Parent.CFrame = CFrame.new(script.Parent.Position)
	* CFrame.Angles(0, 0, angle)
end

0.1 radians / .03seconds is 3.33 radians / second or approximately one revolution per second.