Start by bringing the outdoors in. And what better way than with flowers. If you have a garden, you're in luck. Hydrangeas, coneflowers dahlias, and zinnias make great cutting flowers. But even if you're not so lucky cut flowers are in abundance at this time of year. Including a favorite of mine - sunflowers! Or put some annuals in pretty pots and scatter them throughout your home. Just remember to water regularly.
Textures are an important part of the summer experience. What about swapping your "traditional" area rug for one of sisal? Or decorate with glass jars filled with sand. Use seashells as accessories - and centerpieces.
And if you're really serious about bringing the outdoors in, how about a hammock? Does anything say summer better than that?