Open a word or notepad.

Spam a key away for 10 or 15 seconds.
Using your watch or a clock to time with.

Divide the number of characters spammed, by the time you spammed them.
That is your clicks per second.

Google Search: wowwiki +abilities +class
Fine the duration or cooldown of your spells.

Multiply your clicks per second by the duration/cooldown until you want it to recast.

For a DoT or HoT effect, you want it to run its course, even though you can recast it earlier.
I will generally use reset=target for these.
So if I change targets, the new target gets the cast immediately.

For things with a cooldown, I use reset=combat.
I don't want my Lava Burst to attempt to cast but be on cooldown, even if I change targets.