Use Glyph of Concentration to prevent the highly likely event that the spell will be interrupted due to its long cast time.
Use Arcane Echo (if you are a Mesmer) for double casting. Also consider using Glyph of Sacrifice on the echoed Shower. It will not take an extra 30 seconds to recharge since Arcane Echo will change back to its regular state after 20 seconds. Beware of exhaustion though.
Water hexes that slow multiple foes (such as Deep Freeze) are very useful in conjunction with Meteor Shower, as it becomes harder to escape from it.
Meteor Shower's animation lasts 12 seconds, but only inflicts damage and knockdown on the third, sixth and ninth seconds.
Each knockdown lasts 2 seconds, so a target caught in the Meteor Shower only has 1 second intervals to try to escape or use a skill once the effects begin.