You really need to have the ability to sell cards. I find myself eaiting around a lot for my energy to replenish so i can fight to get coins. In speaking of energy, my other suggestion is being able to spend skill points on a skill that would decrease replenishing times.
 "Learn to Fly 3"){kind=icon}
 "Deep Sleep"){kind=icon}
 "Clash of the Dragons"){kind=icon}
 "Doom Forge"){kind=icon}
 "The Last Stand: Union City"){kind=icon}
 "Epic Combo!"){kind=icon}