Correct Single pole switch orientation
General convention is &quot;Up&quot; is on and &quot;Down&quot; is off. However, for a 3-way switch, &quot;light is on&quot; is on and &quot;light is off&quot; is off, and people manage to live with that every day.
I would recommend that you install your standard toggle switch with the lettering readable from the normal, human, upright position. However, as noted in the case of the 3-way switch, people can function when the toggle isn't in the &quot;normal&quot; position, so there's probably little danger and only minor confusion if you install the switch in the &quot;Down&quot; is on position.
Also, it doesn't matter for a simple toggle which wire (power supply vs load) is attached to which screw. Think of the switch as another piece of wire completing the circuit - it doesn't matter which end is &quot;closer&quot; to the power source and which is &quot;closer&quot; to the load, does it? That's all a switch really is - another piece of wire helping to complete the circuit, it's just that this particular piece of wire makes it easy and safe to break the circuit and turn off the flow of power.