This is how I do a trampoline material. It's not perfect, but it DOES look like a trampoline. Also, this is assuming everything is still Default.

Change the color to black, change the Alpha to 0, and turn on Z-Transparency. Then change the Spec. value to 0.5 and the Hard to 75. Then add a new texture. Make it a Cloud texture, Hard noise, and Color. Change the size and Noise depth to 0, choose an Improved Perlin noise basis, and change the Nabla to 0.075. In the Map Input panel, set the X, Y, and Z size to 0.5. Lastly, go to the Map To panel and activate Normal (Yellow) and Alpha (Yellow) and change the Nor slider to 1. You're done, so render your scene and see your new trampoline.