Also if there is a cleric or paladin in the party make sure you read up on the turn undead rules - they can get tricky to follow at first. And a cleric with a decent turn undead modifier will wipe out an undead encounter with a singel action - very unclimatic.
Another set of rules that is tricky for new DMs (and players) are the grapple rules. I suggest avoiding any grapple type encounters for a little while until the basic combat running becomes second nature to you.
Another set of rules that is tricky for new DMs (and players) are the grapple rules. I suggest avoiding any grapple type encounters for a little while until the basic combat running becomes second nature to you.