Hoping to add nuts and dried fruit.
Google Ina Garten recipes on Food Network. Her bark recipes are easy and delicious; additions and substitutions are easy, as well.
Bark is one of the easiest chocolate treats to make and it always comes out looking great. If you intend to leave large portions of plain chocolate, you may consider tempering so it looks shiny (there are great instructions on the site - I like the microwave method). If you like bark with a lot of "stuff" it's probably not necessary as not much of the chocolate shows. I'd also suggest using a decent quality chocolate as the waxiness of some of the cheaper brands really does take away from the texture of the bark.
Use quality ingredients and make more than you think you should make !