Hello Morningstar,
What kind of grape vines (variety) do you have? [Pruning method depends on the grapes' variety]
How old are the grape vines?
Are you raising them for shade or fruits?
As Lillylac said, the grapes should be pruned when they are in dormant season [and past the danger of frost], depending on location is usually in the winter or in early
spring before buds swell. In Ohio, this done in March.
Two of the widely used method of pruning are:
Spur pruning and Cane pruning. Both can be used to train grapes on arbors.
Spur pruning is used for european table grapes and wine varieties.
Cane pruning is used for American varieties, French-American hybrids, muscadine grapes, Olivette Blanche, Rish Baba and Thompson seedless.
Basically, during the first year, you let the vine grow unchecked (don't try to train growth). The more leaves, the better the root development.
See OSU for more info on
Growing Grapes