If your old shower arm is stubborn, apply a generous amount of penetrating oil (like Blaster 11 oz. PB Penetrating Oil) to the threads where it meets the wall. Let it sit for 15-30 minutes to work its magic. Then, use your adjustable wrench to try again, applying steady pressure. If it's still stuck, a longer handled wrench might give you more leverage, but be careful not to damage the wall.

For a watertight seal, wrap the threads of the new shower arm with Teflon tape 3 to 5 times in a clockwise direction. Ensure the tape covers all the threads and is applied snugly. Wrapping in the direction of tightening helps prevent the tape from unraveling as you screw the arm in.

Yes, turning off the water supply to your shower, or the entire house if there's no individual shut-off, is crucial. This prevents water from gushing out when you remove the old arm, ensures a dry workspace, and avoids potential leaks or water damage during the installation process. It's a key safety and preventative step.

The most common mistake is cross-threading the new shower arm into the wall fitting. Always start screwing the new arm in by hand to ensure it's aligned correctly before using a wrench. Another frequent error is not applying enough (or any) Teflon tape, which leads to immediate leaks after installation.