Start with pruning the dead growth, make sure you are cutting at angle, this helps lessen the chance of infection.
Continue to prune stems to create the framework of how you want the plant to grow. I prune any stems that crossover.
When you shorten the stems keep in mind that it will grow back fuller and denser so you might want to prune some of the side branching stems off.
The bottom line is that geraniums are vigorous growers and very forgiving when it comes to pruning. They use a lot of energy to grow and flower like crazy.
Top your geranium with fresh soil (be careful not to completely cover the stems) and gave them a good drink of water.
When you're finished you can propagate the cuttings by putting them in water.