Shading & Shadows on solar panels
When deciding on a location for your solar panels, make sure no shadows will fall on the solar panel array during peak sunlight hours (say, 9am to 4pm). Not only will shading of the solar panels significantly reduce their output, but also could cause damage. Some solar panel manufacturers advertise panels that can withstand shading but they use internal diodes which in themselves reduce the power somewhat. I recommend simply choosing a good location to start with, even if it means cutting down a few trees or otherwise removing obstacles.
Temperature & Wind loading considerations
As previously discussed, you want to mount solar panels in a sunny and non-shaded location to get maximum sun. But, heat build-up is also a problem. Because the efficiency of solar panels decreases as temperature increases, the solar panel mounting system should allow for spacing around the individual solar panels for air circulation. The idea is to allow air cooling in the hot sun to reduce the temperature of the solar panels. Another consideration is wind loading. By allowing air to flow around the solar panels, not only will they remain cooler, but also the wind resistance of the entire array is less.