The best strategy on level 27 is to match pieces near the earth tiles (or as low as possible). Doing this will not only remove the earth tiles but also start a chain reaction that will allow you to create more power-ups.
Keep a close eye on the field for the power-ups! Don’t rush into using them though – get a couple of power-ups close to each other and explode them all together. This will clear more space and will charge the Lightning power-up faster.