When fighting in the arena, consider your creature's rarity, type, and level. An animal's elemental types and their strength or weaknesses are important factors. The higher the rarity and level, the more damage a creature can execute. A creature must be at level 4 or higher to fight in the arena.
Battlegrounds battles
There are three factors that are important when fighting other creatures in the Battlegrounds; the level, rarity, and type of your creature. For example, Fire is strong against Nature, but weak against Rock. Have at least two types of animals of a high level ready to be prepared for most opponents.
Crops
The fastest growing crops will give you most food. The 30 second foods are the best option, but requires you to be very active to harvest them. When you are about to stop playing for awhile, order the longest crop, otherwise, use faster growing food. Grow food constantly to keep your creatures fed, especially once they are past level 4. Place as many farms on your property possible, and keep them active.
Elements
Each element type has at least one opposing type that it is stronger against.
Crystal is strong against Planet.
Darkness is strong against Crystal.
Fire is strong against Ice Cream.
Nature is strong against Gem, Darkness, Melody, and Water.
Rock is strong against Lightning, Loading, and Darkness.
Habitats
If you have a creature with more than one element, be careful about which habitat to place them in. Creatures must be housed in a habitat that caters to one of their types, but choose the one that is most beneficial to you. For example, Armordillos are Earth and Fire type. Fire habitats stop accruing coins once they reach a 250 limit, however Earth habitats can continue until reaching 2,300 coins.
The Mine
The Mine will become available at level 11. It appears towards the right side of your island. When given the chance to expand, always do so in that direction. The mine allows you to use Explosives to find Runes, which can be used to expand your island.
Water creatures
Reach level 10 to unlock your first water creature, the Frostfang. You can then begin breeding water creatures on your own.
Arena...