Grapevines are used for decoration on garden trellises as well as for production purposes. When growing just for looks, trimming the vines is not necessary. However, if you want to use the grapes for juice or consumption, prune carefully to obtain the best fruit possible.
Choose two or three new growth shoots to keep. Pick the healthiest growth. Look for buds spaced at about 10 inches apart and as thick as your pinkie finger.
Tie the vines you want to keep to the trellis or other structure to train them where you want. This will also keep them out of the way so that you don't accidentally prune them off.
Clip off all other new vine shoots. Trim off next to the main vine. Leave a little nub of the vine. Do not trim flush to the vine because you might accidentally hurt the main stalk and weaken the entire plant.
Leave two or three off the best older vine shoots on the lower sections to keep growing, and clip off the ones that aren't doing as well. Make sure that you have no more than 60 total buds on the vine. Weigh the clippings and keep the proper number of buds, not to exceed 60. Keep 30 buds for the first pound and 10 for each additional. If you have more than 60 after your first trim, keep clipping.