Here you'll find the quick version of 'how to prune a grapevine.' These instructions assume that the vine has been trained competently in previous years; they are also applicable for a vine which wasn't trained properly but is still relatively young (2 - 5 years). With these guidelines you can start to bring your vine back into shape. Older or badly neglected vines, however, will require a more substantialanni cut, called restoration pruning.
1. Identifying the previous year's wood: This includes all shoots grown during the previous year. They are usually yellow-brown, ochre, or red-brown, and have buds 5 - 15 cm apart which reveal their green inside when scratched.
2. First rough ('pre') pruning: Cut *all* of the thin, long canes from the previous year back to about 4 - 6 eyes (buds).
3. Counting the buds: Next year's fruit will only grow from buds on the previous year's wood (aka, 1 yr old shoots = "canes"). How many of these buds per m2 of wall space do you have now? There should be at least more than 20 per m2.
4. Selecting buds: 'Good' shoots from the previous year (canes) will be at least as thick as a pencil and as close to the thick main shoot(s) as possible - not at the end of metre-long thin branchings - provided that your vine has some kind of a recognisable stem framework. Now select about 5 - 7 shortened 'good' canes per m2 from the previous year, which are to be kept, and mark them (e.g., with colored ribbons).
5. Second rough ('pre') pruning: Cut all unmarked shoots short -- flush with the thicker cane, or cut them off completely right back to the main stem (trunk). This will remove about 90% of all branches.
6. Fine pruning: Prune the remaining marked shoots back as follows: in the lower areas cut to 2 - 3 buds ("spurs"), and in the upper areas to 4 - 6 buds ("rods"), so that you end up with approximately 15 - 20 buds per m2 of wall space.