Chest: Reactive procs happen when you are hit with melee attacks. Spell reactive procs happen when you hit with a spell.
Wrists: When you cast a spell that cost mana.
The following can only trigger off the first attack per combat round (if you double/triple attack / flurry and hit the mob X times, you still only have 1 chance to proc) and that attack must land to have a chance to proc. Riposte attacks CAN trigger procs, but only from riposte against the mob you currently have targeted.
Gloves: When you make a barefist attack (no weapons equipped)
Primary/Secondary weapon: When you attack a mob with the weapon.
Shields: When you bash.
Shoulders: When you slam.
Feet: When you kick.
Range: When you bow/throw attack.
Ammo: When you melee with your primary or secondary. Throwing items in ammo cannot proc this way. Proc chance scales with weapon delay, normalized to 20 delay. EXAMPLE: If an ammo proc says 2% chance, it has a 2% chance to proc with a 20 delay weapon. With a 100 delay weapon this would scale up to a 10% chance. With a 10 delay weapon this would scale down to a 1% chance.
BUFF PROCS: Things like Divine Rage, Blades of War, Werefrog Illusion: These scale with weapon delay and do not require the attack to land to have a chance to proc.