A very simple viticultural step that I've always overlooked in the past, mainly because I didn't know that I should be doing it, is to establish an average cluster weight every season. It's easy enough to do: grab 20 clusters at random from any one varietal, weigh them, average the score. Keep track from year to year.
Having a record of average cluster weight swill allow you to estimate your yield early in the season. Once you know your vineyard well, you'll be able to determine how many clusters you keep, on average, per vine, adjusting for weather events and conditions. That way you can prepare tanks if you're in the winery business, or if your a contract grower you can give your customer an accurate estimate.
Cluster weights vary greatly by varietal. But even then, weights of the same varietal can vary greatly based on trellis system, location, weather, etc. Sampling the weight at harvest is the only way to get accurate numbers. But with so much going on at harvest time it's an easy step to forget. I've picked the vidal and traminette already, and I forgot to grab weights on the latter before crushing. Now I've got to wait another year to record this data.