How should I prune my grape plant back ?

I'm like you Lovegreen, in that mine is in it's second year. I have allowed two long stems to spread along the top of my green house. The side (lateral) shoots I've cut back to just four buds. I think that the actual grapes will emerge from these buds. I hope you get lots of advice on this one as I too am a newbie. By the way Massachusetts is a fab place very colourful just now in what you call the 'fall' I spent a few weeks there in the 60's. very nearly stayed !