Grapevines, whether young or mature, require annual pruning to maintain their yield. Pruning is performed in the dormant season after the cold weather has passed. It's important not to wait too long. If the plant is close to budding the cuts will "bleed" excessively. Use sharp pruning shears and disinfect them prior to pruning. Take a tarp into the garden with you in case you need to lay the pruning shears down during the process.
Cut back the new grapevine to two buds after the first growing season.
Remove all fruit as it appears during the first and second growing season.
Prune off all lateral shoots except for the two at the top of the support structure. The first year grapevine should have a “T” shape.
Shorten any growth that goes above the top wire of the support structure before the grapevine’s second year. Cut it back to the wire.
Select the most vigorous cane while the vine is dormant, prior to the second season. Train it up the stake to form the trunk and remove any others.