How do you balance #Fe+H_2SO_4 -> Fe_2(SO_4)_3 + H_2#?
Start by looking at the most complex compound, and balancing around that. In this case, its
We see that we need 2 Fe and 3
The general way to balance is by starting with the most complex compound first, and making sure the rest of the equation conforms to it (it's much harder to try and balance the more complex compound to the rest of the equation).