Know your plant and how it responds to what is essentially an unnatural pruning and training method. The Johnson County K-State Extension underlines the importance of knowing a plant's growth and development habits before you begin pruning.
Prune judiciously while the plant establishes itself to allow it to develop its shape and form so that you can see the main structure. Use sharp secateurs to clip shoots as close to the main stem as possible, with the blades right up against the stem, as advised by the Penn State College of Agricultural Sciences. Clip the shoots growing out from the front and those that crowd the design you're aiming for.
Clip away dead shoots in subsequent years, as well as those growths that don't fit with the planned design. Prune at a time that doesn't interfere with the plant's growth, budding or fruit development. The Department of Horticultural Science at North Carolina State University suggests that you do the bulk of your pruning while the plant is dormant or, if the plant is a fruiting or flowering species, when its growing conditions allow.
Train the plant into espaliers by tying growing shoots to a wall trellis or to supporting wires on the wall during the summer months while the stems and shoots are flexible. Doing so identifies the shoots you need to remove when it's time to prune.