Always make up a good story, and never make rude mistakes, like letting appear people that died one hour ago (unless they are raised
)Never feel sorry for a player. Faults they make are their mistake, and you only react appropriately
DEMAND a good background for the PC´s that makes playing lots more fun, and easier for you to DM
Never ever handle out to much XP, it´s the most costly thing in the D&D game...
Make sure every player can use it´s ability, so don´t create a non magical world, were magic is uneffective, if you have a party of four wizards
Read lots of fantasy books..if you haven´t read the Lord of the rings and the Silmarillion, you shouldn´t be a DM!!
Include humor in your dungeons.. the more fun the better..!!
God bless you and happy playing (Bob Ross saying)