Melt your chocolate in the microwave in a nuke safe bowl for one minute. At this time, the chocolate should be melted but still lumpy, so stir until the chocolate is all melted. I wouldn't microwave it much more, after a minute there is enough heat to melt it completely when you stir it a while.
Once the chocolate is smooth, add in the pecans, pretzels and caramels. If you want prettier bark, reserve a little of the pretzels to sprinkle on the top.
Once it's all combined, spread it out onto a sheet covered in wax paper and if you reserved some bits, sprinkle them on the top and press gently. This really just gives it that "food magazine" look, otherwise chocolate bark in real life has everything covered in chocolate.
Chill in the fridge until it's hard, then break it into pieces. It stays better in the fridge, it IS chocolate after all. It gets a wee bit melty on your fingers at room temperature.