Locate the trunk or the main stem of the grapevine that you plan to prune. Wrap a length of orange work tape loosely around the trunk. This will help you identify which canes and vines to remove.
Clip off all of the vines that extend laterally from the main trunk. Remove them from your work area. Snip off the orange tape.
Examine the main trunk from the bottom up. You'll see bumps or nodes that stick out slightly from the trunk. Tie a piece of tape about an inch above the second node from the trunk bottom.
Remove all of the trunk above the piece of orange tape. Your pruning should have produced a single trunk with no lateral canes, trimmed to contain only two nodes. Those nodes will produce new growth canes with nodes of their own as your grapevine regrows.