A few info:
First, you have to have an obelisk with a proc (just in case you're a very new player. If you're not, ignore this)
a proc runs for 5 seconds and has a cooldown of about 5 seconds if you have your cooldown reduction capped. So it runs for 5 seconds, wait for 5 seconds and after that it will have a chance to proc again (take in mind that the proc has a percentage to trigger, its not 100%)
there are skills more prone to trigger the proc. The more hits the skill has the higher the chance to trigger (cause the proc has a chance to trigger PER HIT). Example: quicksilver's 4th skill has more hits than 5th so its more likely to trigger the proc. That way he can almost everytime trigger the proc on 4th skill if you do the rotation 5cancel into 4.
Proc triggering varies from character to character. Just analyze their skills, see the one that does the most hits/damage and test rotation to trigger hit.