Energy is vital in CastleVille, primarily for completing tasks, such as building, or collecting taxes. Energy recharges automatically over time, to a maximum position of 25. You earn 1 Energy for free every 5 minutes, but if you want to get it quicker, there are a few techniques for doing so:
How to get Energy:
Play the game: You have a chance of earning 1 Energy every time you click to perform an action in CastleVille. Obviously, because each action costs 1 Energy to perform in the first place, this effectively only cancels out that initial Energy cost. It's still nice to get though.
Whenever you level up you receive a total refill of all your Energy stocks. Because of this, it is a good tactic to use up all your Energy just before leveling up so as not to waste any of this generous reward.
If you defeat Gloom Beasties, you have a chance of earning 2 Energy each time, while the action of fighting them also gives 1 Energy out occasionally.
You can get Energy by cooking Food in your kitchen.
Post and Read Energy Requests:
Keep an eye out for a notification allowing you to post Energy requests to you Wall. This will prompt friends to gift Energy to you, which can be crucial in keeping your supplies high. Similarly, if you click on other people's Energy requests, you in return get an Energy boost.
Every action you perform in your Neighbors' kingdoms has a chance of rewarding you with Energy. Once you collect a certain amount, however, you hit a limit and can only receive coin.
Neighbors Killing Beasties:
It is a good tactic to let beasties roam around your kingdom until a Neighbor comes in and defeats them for you - you can then collect the Energy reward that this normally gives, without the Energy outlay of having attacked them yourself. With enough friends this can be a really good tactic.
You are able to purchase Energy using Crown, or basically through spending real money. If you're very desperate for it then it's not a bad idea, but you should be able to get it for free easily enough using the tips above.