In Little Dragons, coins are the main currency in the game. You need coins if you want to buy almost all of the buildings in the game, as well as all of the base dragons, and all dragon habitats. Energy is the food that the dragons feed on in order to level up. The more energy you have, the higher you can level up the dragons, meaning that they will earn you more coins. Experience points are needed to gain levels, and when you gain levels, you can unlock new dragons, habitats, buildings and building upgrades.
To get a ton of coins, instead of waiting for the dragons to collect, set the time ahead by an hour or two, and then go back to the game. Then, go and set the time back to normal, and then go back to the game, and the dragon habitats will still be filled up. Now, collect from them, and repeat the same trick over and over.
In addition, send dragons on quests through the Viking Agency, and instead of waiting 24 hours for the quest to finish, set your device time ahead by one day. Now, when you get back, the quest that they went on will be complete, so tap on the Viking Agency to collect on it. Now set the time on your phone back to normal, start another quest, and repeat the same thing. This trick can earn you a ton of experience points, as well.
To earn a ton of energy, first, buy the maximum amount of energy wells that you can for your experience level. Set every single one of them to the longest energy purchase, which is half an hour for the small well, and several hours for the big well. Then set the time half an hour ahead (or however much time you need) and go collect on all of them. Then go set the time back to normal and you can start the whole trick all over again as long as you have enough coins for it.
To get a ton of experience points, use that energy above to feed your dragons over and over and over again, as each time that you feed them, you will earn experience points. To make it happen even more quickly though, use those coins that you earned to buy expensive items, such as expansions, or to clear off massive amount of rocks, pines, big pines and rock moss. Then set the time ahead on your device and go back to the game, and collect the experience. Repeat this for as long as you have coins to make it happen.