1. Bugs-Make sure your mount is in a bug free area of your home. I know guys who stick mounts in their garage(usually because of the wife) and that is NOT SMART if you want your mount to last! Moths, beattles, etc...Will all eventually get to your mount, no matter how well it's preserved!
2. Water-High moisture/humidity areas will actually change the chemical balance of the skin and may cause it to decompose. Also, keep your mounts away from high heat areas(fireplaces, vents, etc)...You want to keep your mount in a steady temp. area if at all possible!
3. The Sun!-Any sunlight that hits your mount will fade the color of your feathers, fur, skin, etc...Keep them in a shaded area!