What threw me about Dispelling is that it doesn't matter where you click. You don't have to click inside the circle when it's over the rune, you just have to click period.
Effectively, you're playing a circular version of Dance-Dance Revolution -- you want to click when the circle overlaps with the rune exactly. Missing a rune entirely will re-lock every unlocked rune immediately, meaning you'll have to do it again. Hit a bomb or run out of time, you detonate the ward.
The goal is to get all the runes clicked at once. I don't think it's possible for the order you click the runes to matter - as long as you're clicking them in order around the circle (and avoiding the bombs), you should dispel it in a revolution or two.
Both the speed of the rotating ring and the time you have to activate all the runes change with level, with the speed increasing, and the time decreasing. Improving one's Dispelling skill has the opposite effect.