what variety do you have and where is it planted.
I have Blackhamburg in the greenhouse. the roots were originally inside the greenhouse but they will be well outside now. They need plenty of water too.
when the fruit sets remove about 1/3 of the grapes evenly from each bunch. then about a month later repeat again. this ensures fewer but bigger grapes. As they begin to ripen I remove any leaves from infront of them so they get plenty of indirect light.

I prune mine at christmas when it is fully dormant. I leave 3 main lead stems and prune eveything back.