Take the pretzels, M&M's and sprinkles out of their packaging and place in small bowls or set near your pan. You'll want to have the toppings ready to go, as once the chocolate bark goes on the pan, you'll have limited time to work.
In two separate microwave safe bowls, add the chocolate and vanilla bark to each bowl, keeping them separate. Microwave each bowl for 1 minute, stop to stir, then continue to microwave for 30 second increments until completely melted.