It is a good idea to gently hold the valve with pliers so the tube isn't dealing with the torque. It isn't essential, but a good idea.
I have not had leak problems when I properly tightened the valves, so I don't Teflon tape the threads.
Teflon tape is way thinner than electrical tape and can slide through most rim valve step holes and keep the rattle away.
TeflonTapeVAlveSm.jpg