Drive the T-posts into the ground 1 foot deep at both ends of the rows in which you plan to grow your trailing blackberries.
Wrap wire around one of the T-posts, 3 feet from the ground. Stretch the wire to the same height on the opposite T-post and attach it there.
Wrap wire around one of the T-posts, 5 feet from the ground. Stretch the write to the same height on the opposite T-post and attach it there. When this step is completed, you'll have two pieces of wire running across what will become your blackberry thicket.
Arrange the blackberry canes through the wires as they begin to emerge. Arrange the canes so that they will grow to the top wire.
Weave the canes back down to the bottom wire and back up to the top wire, filling in the spaces between canes on the wires, as the canes reach the top of the wire and continue to grow.