Hello Fellow DragonVale Friends,
From what I've noticed (lvl 18 and worth $18 Million) you breed dragons based on the flags on the eggs page. There is a left and right side in the breeding section and it's important to add the correct dragon on each side to improve your chances of getting what you're looking for. For instance a chrystal dragon can be made from a lightning dragon on the left and an earth dragon on the right. They are an awesome source of cash. The earth habitats hold 75,000 Dragoncash as opposed to the plant habitat's 500 DC. I have not paid gems for any of my dragons yet and I have them all except the rainbow. That one is proving difficult to breed as it is a 1% chance you will get a rainbow dragon. You can always look at the time it takes to breed or incubate (they are the same amount of time) by pressing the "Incubate" button. It will give you the time left breeding and the number of gems it costs to speed it up (one per hour of time) then simply press "No" if you don't want to use the gems. You can check the eggs section and see how long the dragon you are looking for will take. The rarer dragons typically take 8 hours. The rainbow takes 48. Buying and placing the DragINN from the 'Decorations' section earns you XP and a higher island value. They also have a small footprint so you can do it many times. They cost 100,000 DC. If you look at the top players, many have them everywhere. I love this game! Hope this helps. Any questions, feel free. Also, if you have advice for the right combination for a rainbow dragon breeding, please, let me know. Happy Valing!