Hey,

I wouldn't recommend you to play as earth main in the early game, this is because the earth main is a too much supporting ninja and he is not the best at the start, since he needs stronger ninjas, other than the ones you can acquire at the start to make him work with. Only very specific and very few options working for him. In the late game however, he is awesome. I'm suggesting in general to choose any of all the other mains until you acquire some more better ninjas. Any other main is working, especially water main and fire main. They're both great for the start and I'm suggesting you to even use them as position one. I got a small formation guide in which I worked on few months ago which is under the link, which I also hope to be useful for you at the start: https://goo.gl/DMdELn

Hope it helps ~