I started running a new group through a D&D campaign the other day. I'm always nervous when I have to DM. It is a lot of responsibility and requires a lot of prep work. The biggest thing is that a DM can NEVER prepare for all the outcomes. Your party members can go completely off the rails in unexpected ways. You may think you know your party and plan for when they do go off script. It doesn't help. They will never do what you think they will. As the DM you have to plan contingency plans for when they do something you aren't prepared for. That was the case for us. We basically got to go through the lead up to where everyone meets, and all hell broke loose. 3 hours and still in the introductions... They have just barely met each other and chaos ensued.
Shantz - Director of dice rolling failure and comedic timing