One way to create interest in an arrangement is to modulate to another key at some point. A common technique is to place the modulation about 2/3 of the way through the chart so that the climactic point of the music coincides with the modulation.
Deciding whether a modulation is necessary in an arrangement is up the arranger (and singer if written for vocalist), but always keep in mind the benefits to how a chart will come across to the listener by using modulation.
I had a class member ask me recently about how to set up a modulation, so this lesson covers those concepts.
Please post any questions or comments you have below.