There are a few, pretty obvious measures you can take to preserve charcoal drawings. Charcoal is a raw, spontatenous form of art which is particularly suited to capturing a moment in black and white for eternity. We still have charcoal sketches from past masters to admire, despite it being a very delicate medium to preserve. In fact, a well- cared for charcoal drawing will last centuries and will be kept by generations in your memory and honor. However, you need to take extra care in handling the suface of the drawing because, despite it having been treated with a professional fixative (not hair spray!), it can and will still smudge. Use white gloves whenever handling it, as the grease from your fingertips can  make the paper oily and dirty. Frame it using UV or art glass if you can, and avoid placing it in direct sunlight. Basically, the less you touch it, the better!