According to the professionals that produce the touch up spray paint, there are 2 things that will make a big difference in the use of aerosol spray paint.

1.  Shake the can vigorously for a long time. 
     When you think you've shaken it enough, do it longer.

2. Apply 3 or 4 coats to the item you are painting.  This will help greatly to reduce the amount of fading that can occur.  It's not a bad idea to prep the item to paint by roughing up the surface and making sure it's clean and dry.