A. Blackberries can be a bit confusing at first. You are managing two stages of growth with blackberries; the canes that emerged from the ground and grew last year (two year old canes) and the canes that will emerge this year (one year old canes).
Fruit this year is produced on canes that grew last year (two year old canes). Canes that grow this year (one year old canes) produce fruit next year.
When canes produce fruit, they must then be removed or pruned to the ground. The easiest way to do it is to remove them soon after you pick the fruit.
If you wait too long to prune it can sometimes be difficult to see which canes to prune out and which ones to leave for next year.
In our climate, vigorous blackberries seldom reach the heights they can get in milder climates. However, if you have a vigorous blackberry that will get quite tall then cut the tips off of the canes when they reach about four feet in height. This helps to make them stiffer and more capable of carrying a fruit load.
Some blackberries grow along the ground and others grow more erect. If the one year old canes grow along the ground then you will have to wrap them around some trellis wires. If they are fairly erect in growth you may not need to.
A bit of a disclaimer. Blackberries do not do that well in our hot desert climate with our highly alkaline soils and salts. We have followed the advice of some work done in Yuma by the University of Arizona and grew both Rosborough and Womack varieties in Las Vegas which are erect forms. Even under good growing conditions they seldom get above 5 1/2 ft tall. However, Brazos did not do well for us. Others that have not performed well in the valley include Arapahoe, Navaho, Cherokee, Apache, and Kiowa. Some people have reported success with some cultivars but upon checking these plants are only one to two years old and they frequently fail after that. You will need at least five years of success, as we do at the Orchard, to call it a "success" or plant it as a biennial.