Provide transcriptions of important but illegible documents. Buy display cases from a manufacturer. If it has its own light source, it should be mounted on the outside of the case. Choose cases that conform to the architecture of the room. You can also use wall mounts and freestanding panels to display materials.
Originals are best, but sometimes copies are best suited to the needs of the show.
Use them sparingly, and only when done well. Not all photos reproduce well. Employ a skilled individual to do the photography and printing. For large exhibits, make scale drawings or models. Be sure to take accurate measurements of the exhibit areas and the objects being shown.