Being a DM requires a variety of skills, but to keep things simple we will be focusing on 4. I call them the four pillars of DMing: Scheduling, Leadership, Rules Knowledge, and Flexibility. Some experienced DMs would say there are more skills needed than these, and that is true. However, good skills in these four categories are enough to run great games that your players will love. --Kirk Melhuish
While it might seem obvious, one of the jobs as a DM is getting everyone to show up to the session. The best practice is to make one night of the week when everyone is free D&D night. Make it clear to your players that they should try their hardest to be free every D&D night, but also add that life happens. Be flexible and don’t be afraid to move the night to another one if someone can’t make it. Each group deals with people canceling differently, and it is a good thing to bring up during a Session Zero. Some groups might just cancel the session when someone can’t make it or try and reschedule. Other groups might still play if one person can’t make it but will cancel if two can’t be there. Do what works best for you and your players, but try your hardest to play come D&D night.
The other aspect of scheduling is communication among the group when people can’t make it to D&D night. While discord is where most of this will happen it is good to have the phone number of each player in your contacts. If it’s game start and someone is not there send them a PM on discord. If there is no response a quick call usually solves the issue.
Tell your players that if they know about a conflict coming up to tell everyone in advance. This gives everyone time to reschedule and also helps you change any of your prep. Maybe 5 Kobolds in that forest fight you have prepared is too many if the Barbarian can’t make it. When you are experienced these changes can be made on the fly, but out of the gates it’s good to have time to make a plan.
While it might seem intimidating at first, an important DMing skill is commanding the attention of the table of PCs during the session. You sit at the head of the table behind a DM screen, and when the session starts everyone will look to you for direction. If this thought makes you nervous don’t worry, it’s normal. As the DM you are putting your work out to the PCs for them to take in and form an opinion on. Another word for this is stage fright, and it’s something performers often suffer from. Usually it goes away a few minutes into the session.
One of the hardest skills as a DM is commanding the attention of the players and using this to drive the game forward. Be ready to talk. A lot. When you start a scene assert that you are the one talking. If you’re interrupted either tell the player who did so that you aren’t done, or if the description is enough allow the player to continue. If you are in the middle of a scene and need to move forward verbal shortcuts like “and so” and “so meanwhile” work well to insert yourself into the conversation to make your point. It will take practice to know when to talk and when to hand off the scene to the players. Out of the gates it can be helpful to prewrite any descriptions that you know will be needed. The balance between improv and prewritten descriptions depends on the individual DM. As you run more games you will find what works for you.
An easy tool to keep player engagement is to use character names during session when talking about in game events. I usually say to try and do this as much as possible during the session. It works surprisingly well to also keep the players in the head of their characters. If you are forgetful like I am, write all the player and character names down on something that is easily referenced. A post it on your monitor or DM screen works well for me, but you could use a note card, google doc, journal, or whatever else works in your case.
It is quite easy to get side tracked and go on tangents for long periods of time while playing D&D. While this is part of the fun, it is your job to bring the focus back to the game. A good way to do this is to rewind a bit and prompt a player to continue what they were doing. “Nirka, what did you say to the guard again?” is a good example. This makes it easy to get back to the scene. If you don’t remember what exactly just happened prompt the group for the last thing that they did. “So what is your all’s plan here?” is a good one to use in the middle of a scene.
One of the most important roles of the DM is to referee the rules at the table. My biggest piece of rules advice is to understand the rules for a PC before trying to become a DM. It is much easier to become a DM after playing a character or two in a game as a PC. If this is not an option you will have to work twice as hard to learn how both PC gameplay and DMing works. It is possible but quite hard. Reach out to me if you need to go this route.
The golden rule of D&D is that the word of the DM is the final say on any matter when it comes to rules. Even if it directly goes against what it says in the Player's Handbook or Dungeon Master’s Guide. While this can be a useful tool to introduce cool aspects into the game it can also take away from player enjoyment. An example of this might be a player that has an ability or class feature that doesn’t work Rules As Written in your game. In this case make that clear during the Session Zero so they are not surprised by this. These changes, called Homebrew, should always be clearly told to the party. I often make a document for them to reference so that it can be read in sessions at the table. Remember that the goal of D&D is to have fun, so do this sparingly.
It can be helpful to delegate rules searching in game to a PC that you trust. These “Rules Lawyer” players can be an easy way to check a ruling in the middle of the session while you, the DM, keep the session moving forward. This can also work against you, as these players might call you out for breaking the rules. If this happens it is up to you whether to change what you did, or cite the golden rule and keep the ruling.
When I first started out DMing a friend of mine told me to assume that battle plans do not survive first contact with the enemy. While this usually applies to fighting it is also true for D&D, but in this case the enemy is your players. No matter how well you plan your players will always find ways to surprise you. Ask any DM and they will tell you the same thing. I have a story to illustrate this from my first ever game of D&D. My DM, Rich, had us crawl through a kobold infested cave to get back a stolen relic from the local inn. When we finally got to the end of the dungeon we found the nests of the Kobolds. They had eggs in the, as nests would, and Richard didn’t even think twice about adding them. But then one of the PCs, Bobby, asked if he could take the eggs and raise them as his own. I will never forget Rich’s reaction, he was not prepared for this at all. What started off as a simple description of a room turned into a much larger thing that it was. As I said, battle plans do not survive first contact with the enemy.
Every DM has a different way they deal with being caught off guard, and the more you do it the easier it becomes. If you are new and are caught completely off guard don’t worry. Don’t be afraid to tell your players that you need a few minutes to think about how to respond. In the example I gave before it was Rich’s first time DMing, and after the Kobold incident with Bobby he ended up taking 10 minutes to figure out what to do. This kind of planning is essential to running amazing games as a DM. Be flexible, if your players are starting to go off the rails start planning right away. If you want to be sneaky, tell them you need to run to the bathroom while they plan, giving you a few moments alone to figure out what to do. Always try and stay one step ahead of the party in session and it will be hard to be surprised without being ready.
Even though battle plans do not survive first contact with the enemy it is still good to prepare for the session ahead. There will be a time however when you’ve made a great plan for a session and your players go and completely ruin them. While this can be quite upsetting at times, don't fear, your idea isn’t completely lost. The illusion of choice is one of the best tools in a DMs toolbox and can often hold a game together. So what is it? Simply its a situation that, while the players might feel like they have a choice, they will always end up where you wanted them to in the first place. An example would be a room with two doors, one of which is the place the party needs to go. Both doors actually lead to the same room, but the players have no clue and feel like there was a choice. Another example might be some important NPC that the party needs to meet in the guardhouse. If the players instead decide to go to the town hall or the inn, just move that NPC ahead of the players to one of these places so they still end up meeting them.
While technically not a pillar, imagination is the most important part of being a DM. Think back to when you were a kid, swinging sticks in your backyard and pretending to be aboard a pirate ship. D&D is a similar experience, and you the DM are the one to shepherd that experience forward. I always say that when I DM I imagine the scenes in my head and just describe the visuals to my players. Your job is to share that picture in your mind with the party, and have them interact and respond to it. As said by Matt Coville, it’s the most fun you can have with a brain.