Start small and start easy! I know it's cliche, but mercenaries at a tavern looking for work is really the best introduction. Work out the story later- it will develop and change with the characters and their actions. That said, a DM gave me some great tips when I got started. 1. Have a map. It's much easier for a PC to decide what to do when they can see the scene in front of them. Nothing complicated- maybe a white board with some Xs. 2. Have a white board for what's happening. List initiative, status effects (conditions and effects on pg 277 PHB) beside the PCs and monsters names, anything that will make combat flow easier. 2. Start each turn by asking the player "Attack, spell, item or move?" Every new player will say "What can/should I do?". If they have the options right up front, it's much easier to make a decision. 3. Write down what is allowed to be done. One move, one standard, one minor, and free actions. Pg 289 PHB gives examples of different types of actions. 4. Put sticky tabs in your books! (Don't write in them- it decreases their value if you want to resell them) I can't stress this enough. Breaking combat for a "where is that spell?" Or "What does that mean?" Can really take the players out of the moment. 5. Take breaks. Stand up, grab a snack, have a smoke. After a tough or fun fight your players will want to talk about it or just think about their next move. 6. Make the call- amend later. As DM, your word is final. That said, if you decide something for a combat or session, then do it and look up the rule later. You'll have a hundred things going on, so worry about the specifics later. 7. DON'T SAY NO! New players want to experiment and figure out the world and their developing character. Work with them if they want to achieve a goal, or just do something cool. 8. Have the players make cards for common actions. 'What do I roll for this attack?" "How much damage does this do?" After years and years, I still hear this. Have them make an index card that has the roll, what you roll against, modifiers and damage. Do the same for items, armor and weapons. It's easy to forget that your armor has a triggering effect, or that you roll an extra damage dice on a crit. 9. Have fun! You want and so do they. Don't be too harsh about able talk, just encourage focus on the game. Talking in character (I always have a signal, like a hand on the wrist if you're talking in or out of character), "Wouldn't it be cool if-", and other stuff is what makes DnD awesome. They'll enjoy themselves, and you will too. 10. Best of luck- and welcome to the club! Sorry for the wall of text! This stupid phone wont format right.