Hard mode has the spheres going in two different directions. This makes it a little bit easier in the beginning because you can get bigger chain. When marbles are being destroyed on one side, expand the chain by shooting a marble into the other side. It is easy to get a twelve or better chain this way. The strategy mainly for Hard mode in the beginning is just to group pairs of at least two red, at least two blue, at least two red, then destroy a set in the middle of this arrangement in each path.