In addition to Desmer's comment : For those of you who are having trouble on level 10; after hiring both miners, it is actually better NOT to send waves early, because you the two miners will generate a higher income (I'd say around 60-80g) than the 30 or so gold you get from sending the wave asap. Hope it helps :). . . I have found something that when combined with this makes it easier (In the houses closest to both miners add at least one mage and the rest something ranged and make the one mage a healer so then the miners will be healed after a fight) Hope this makes it a lot easier.
 "Incursion"){kind=icon}
 "Disaster Will Strike"){kind=icon}
 "Kingdom Rush"){kind=icon}