I suspect your climate is sub-tropical. I am in a cold winter area, there are bonsai growers in the Azores, if you can, join, or at least attend without joining a few local bonsai club meetings and ask someone who grows in your climate about timing for pruning. But I'll take a stab at your question. My answer is assuming most trees have a seasonal growth pattern, that follows a winter, spring, summer, fall pattern. But you might be warm enough that the pattern is really a wet season - dry season pattern.
First - the best answer to when to prune is there is no one ideal time, and ''best practices'' or ideal time is species specific. So any generality will have many exceptions.
Generally for deciduous or evergreen broad leaf trees there are two times of year for pruning, In late winter, just before beginning of spring growth. The second season is early summer, after spring growth has extended, and begun to harden off close to the trunk but is still actively growing at the ends of branches. For some trees, the ''late winter'' pruning can be done as early as autumn, through to spring. There are species specific exceptions. For example, Princess Persimmon is pruned late autumn or very early in the winter. If you want to see flowers on a Satsuki azalea, no pruning after middle of summer, though for a well developed azalea you will thin out the number of blooms to balance the tree's strength sometime in autumn. Azaleas are normally pruned after flowering in late spring - early summer.
Nurseries, public utilities, and other commercial operations have other considerations beyond just the health of the tree being pruned. Autumn is not the worst time to prune, they usually have to pay a crew, and keep them busy all winter, so they will prune at less than ideal times for monetary reasons. With trees in the ground you can get away with some things that a tree that is all ready stressed by being forced to live in a bonsai pot will not tolerate.
Some species are best only being pruned while in active growth, (usually summer) such as the more tropical ficus species. (not carica). Where the temperate growing Ficus carica is best pruned while dormant.
So when you are trying to decide what to do with a specific tree, start a new thread with a picture of the tree and the name of the species, I'm sure the BNut's here will be happy to give you pruning advise specific to that species.
Also check the tutorials in the New to Bonsai threads.
