Andy: As I have learned over the years about things discussed on this forum, there are usually a number of ways to go on any aspect of wine-growing. There is much value in various methods being helpfully described by the good folks on this forum, as it presents options to consider for your own situation -- depending on the unique challenges you are facing, and other factors like time availability, resources, etc.
Where I live there are usually pretty severe disease pressures because of our heat and humidity. Last year's July was an exception -- heat with low humidity days and only about an inch of rain for the entire month. But this year's July has brought over six inches of rain, constant high humidty, and some unusually warm overnight temperatures. The rains have often been ill-timed cloudbursts (e.g., right before sundown so things stay wet for more than 8 hours). This July has had more robust-than-usual shoot and leaf growth, resulting in a thick, dense canopy. Even with diligent regular spraying every 7-10 days (I stick to the basic Mancozeb or Captan, plus sulfur) the mildews, bunch rot, and other usual bad guys can get started in the blink of an eye.
So for my situation, it is imperative to keep making sure there is good air flow around the fruiting zone, as it not only helps with drying off dew and rain but also helps ensure much better coverage with my spraying.
The summer begins with a good shoot thinning, when they are about 5-10 inches long, aiming for a comfortable spacing. In our climate, for red vinifera 3-5 shoots per foot is recommended. The recommended distance between shoots can differ by climate, by whether it is red or white, by whether it is hybrid or vinifera.
After shoot thinning is done, for me it's all about leaf pulling (and sideshoot removal).
Right now, as veraison is about to start here for my vinifera (probably by the end of next week), I have very few, if any leaves near clusters, none below any cluster and probably only a few nearby to the side. I'm pretty ruthless, certainly more so than would be warranted in a climate with less disease pressure. Throughout the summer I also remove any side-shoots in the fruiting zone, and most of them elsewhere, too.
For me, pulling leaves is a gradual process, starting a few weeks ago, post-bloom, with an initial pulling of all the leaves in the fruiting zone on the east side of the vines (so the morning sun can dry off any rain or dew). Then, over the following weeks, I gradually remove leaves (starting with the lowest) on the west side as the fruit begins to set. All summer, on every stroll through the vines (including with a glass of wine in hand...) I find myself yanking a leaf here and a sidewhoot there if it seems to be encroaching too close to a cluster. At the very least you want to avoid leaf 'overlap,' and may want to be more ambitious than that, depending on the situation.
The advice I usually see is to try and keep -- depending on who you read -- anywhere from 12 to 15 to 18 to 20 leaves on a shoot per cluster. Oldtimers who've dealt with this particular climate's heat and humidity tell me that by harvest day they usually have some cluster-bearing shoots that may be down to around 7 to 10 leaves. Other factors to consider is what grapes you are growing and how much (and for how long) you need to think about avoiding sun burn (a long topic unto itself). Trade-offs always seem to be involved.
Again, there are many, many different ways to do it than what I just described. It's all about your particular situation in terms of your climate, nature of disease pressure, types of grapes, and other issues like your time and resource availability.
