Lior assimilated spice blending to creating a guest list for a party. You should be careful who you invite, because you don't want one spice to overpower all the others. It's all about balance, so that each of the spices "personalities" opens up to each other. In our blend, we added clove, allspice, annato seeds, mustard, cardamon, anise, cinnamon (a powerful spice that should be used sparingly), celery seed (a natural source of sodium), and caraway seeds.
It seemed as if there was no "wrong" spice to add. However, those new to spices can always start by experimenting with the spices used in traditional spice blends to make homemade Chinese five-spice or garam masala.