Make sure that it receives some sun, make sure that it gets adequate water, fertilize sparingly around the dripline (1/4 cup of cottonseed meal in spring and early summer for a 1gallon plant), prune right after flowering and apply appropriate winter protection techniques for your zone (see the link below). Flower buds begin to grow during the summer so make sure that it is happy during that critical time.

I hope that helps,
Luis

Here is a link that might be useful: Overwintering Hydrangeas