During the time when you tree has just expressed all of its early energy
(spring time).... defoliate your tree and the new leaves will be much
smaller when they reappear. This is only for a HEALTHY tree. If it has
weak growth let it get energy over the next year. If it did not bud out
well and seems weak do not attempt this. The key is that when you
defoliate the tree, it has less energy to create big leaves so smaller
leaves are produced. When dealing with evergreen trees you need to
continuously defoliate the bigger leaves leaving the smaller ones intact.

Jim