Be very sparing with the use of your mighty power meter, and save it for when the going gets really tough.
Don't forget to upgrade your abilities evenly as you play the game.
Don't forget that you can upgrade your temples too.
To place a defensive unit on your temple island, tap on the creature you want to use and then drag the icon towards one of the glowing dots on the island. It costs coins to place each one.
To unlock defenders you'll need to reach various progress milestones in the game, such as reaching a certain level on a God's island.
Struggling to keep track of multiple assaults!? Tornado ability is very useful for that as tt'll whip up any targets that fall into its path, and keep them crowd-controlled for the duration of the spell's effect.