The optimum number of grape bunches on a vine depends on the vine spacing and the variety; this number is in the range 10 to 24 bunches (from 5 to 12 'fruiting' buds) per square metre of land occupied by the vine.
For example, after winter pruning you may leave 20 potential 'fruiting' buds (2 long canes of 10 buds, or 10 short spurs with 2 buds each, one-year-old wood) each of these should develop 2 flower-clusters = up to 40 potential bunches on a vine. Note: any cane left after winter pruning must be at least pencil thickness (8mm diameter).

In the first cropping year it is wise to leave a maximum of about 10 bunches to fruit on a vine. Leave the lower bunch on each shoot as these will be more advanced, but don't pinch out anything until after flowering is over (in July) as the berries may not set properly.

Cane or Spur Pruning:-

Cordon training has 'spur' pruning, with short or fairly short fruiting canes (pruned to 2 to 4 buds). 
Cane pruning is long 'replacement' canes (say 10 to 14 buds). With certain varieties you don't get strong enough growth from the lower (basal) buds, so these lower shoots will not be thick enough for use as replacement canes, you then need to prune to leave a few short spurs below the replacement canes, and hope to use the canes from these short spurs in the subsequest year, in order to keep the replacement fruiting canes as close to the head as possible; there may be no grapes formed on the shoots from the short spurs.

There are many varieties where most grapes form on the furthest/strongest shoots, and it is unlikely that you have much (or any) fruit from the weak lower/basal buds, even if you bend the fruiting canes sharply between the second and third bud (to give 'apexal compression') to try to increase the sap flow to the lowest/basal shoots. With these varieties (usually the strongest growing ones) all the strength of growth goes to the shoots nearer the end of the long cane, and the grapes formed are on these furthest shoots. It may seem that by spur pruning these varieties you will force them to produce grapes on the basal buds, but that's not my experience; one year I spur-pruned my 1000 Dornfelder vines and not a single flower cluster formed on any of the vines. Solaris poses a similar problem.
With such varieties a technique that can be of assistance is 'girdling' of the long canes, between the second and third buds; I sell special girdling pliers, with instructions for use.

Bud rubbing:-

After mid-May (when any danger of frost is past) rub off any excess or unwanted weak buds or downward growing buds, and rub off any 'water shoots'; these are shoots growing from the main stock or old wood. It is a waste of time rubbing water shoots off too early as new ones will form.

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