These are the guidelines I teach and follow:

• Keep your pick in between your index and thumb and use your middle finger to tap so you can go back to picking if you need to.
• Make sure your shoulder and arm are relaxed.
• Most of the tapping power will be coming from your wrist.
• You will be “bending” or applying your force from your knuckle joint at the base of your middle finger.
• Aim for a little lower than the center of the fret.
• When you tap, apply a large amount of force and pull off to sound the note.
• Make sure your palm is muting the strings you are not tapping (or have some kind of cloth at the neck of your guitar).
• Practice recoiling to gain speed.
• You will only use your forearm when you switch to different strings.

Hope this helps!