Of course, by far the most reliable way to get energy - and the way you'll want to avoid using, if possible - is to buy it using gems. Gems here are the game's premium currency, and, well, that means they cost real money. Ugh... But of course, you will get rewarded with gems occasionally through game progress, and you can of course use them as a free energy boost in times of need.
It takes time
Well, erm, how patient are you? I know, I know, this is a terrible tip, but you and I both already know that one of the best and most reliable ways to get energy will be to wait. Here's a suggestion: try playing a different mobile game. Another King game? Or perhaps something from Supercell? There are loads of options.
More modes
Hey, here's another thing you can when you have run out of energy: play a mode that doesn't require energy. That's right! Game modes outside of campaign actually use different forms of energy, so you can dip into the treasure caves, take bounties and look into the dungeons while waiting for your campaign energy to return. As you level up you'll unlock even more game modes, and events will be added to the game over time, giving you plenty of other distractions.
Very rewarding
The best, or possibly quickest and least reliable, way of getting energy will be through quest rewards, campaign progression, and your daily log in bonus. When moving through the campaign you may occasionally get rewarded with energy, same with quests. Alternatively, you might receive gems, which you can buy energy with. You won't be prompted to open your daily chests and grab your log in bonus, so make sure to do those every time you log into the game.
