The technique of defoliation is a widely accepted method of reducing leaf size and increasing twiggy growth in deciduous trees as it essentially forces the tree to put out a second and more numerous flush of growth or in effect an additional season of growth from the leaf axils which remain.
In particularly strong growing trees it is useful to defoliate also as it allows the grower an opportunity for easier wiring without leaves to get in the way limiting vision. This second flush of leaves exhibit autumn colours which is said to be due to the fact that they are weaker and as you have duped the tree into thinking it is autumn.
So now that you have the background on defoliation this is how you can perform defoliation on your tree. Using a pair of scissors or special shears designed for defoliation, cut off each leaf leaving the leaf stalk behind. The reason you leave this leaf stalk behind is as this will support the new growth sent out by the tree and which will emerge from the dormant buds at the base of the leaf stalk. You can expect the new growth to take about 3 weeks but will depend on the vitality of the tree. This last comment should be considered seriously as it is not advisable to perform a complete defoliation on a tree which is not healthy or to perform repeatedly on the same tree year after year.
There are a few risks involved with complete defoliation. As mentioned already if the technique is applied almost as routine year after year on the same tree the tree health or vitality will most likely suffer. It is possible that you could experience some die-back in your branch structure, particularily the finer twigs by removing the entire leaf. Lastly the profusion of the growth which emerges after complete defoliation can result in random die-back unless it is brought under control, or thinned out a bit.