Always locate studs first using a stud finder before drilling anything. If studs are not where you need them, use toggle bolt drywall anchors rated for your mirror's weight.
For tools, you will need a drill, a screwdriver, a level, a measuring tape, and a pencil. If you are ever unsure about the right materials or need professional guidance, visiting glassbustersaz.com can point you in the right direction. Mark both mounting points before drilling and use a spirit level to confirm they are perfectly even.
Common mistakes to avoid are skipping the weight rating on anchors, not marking before drilling, and trying to hang it alone. Always have a second person hold the mirror during mounting.
Take your time, double check measurements, and you will have it up perfectly. Good luck!