Yeast is a delicate organism and requires some care before it goes to work in your wine. It is important when re-hydrating the yeast, to not “cook” it with too hot of water. You should re-hydrate the yeast at 50°F-86°F.
When pitching the yeast into the grape juice, the must, make sure that the temperature is in the 58°F-62°F for white wine and around 65°F for red wine. Do your best to make sure that the temperature does not fluctuate more than 10°.