The DM's primary responsibility is to make sure that everyone is having fun. If that means everyone is constantly engaged in combat, great! If it means that the group is skulking through a seedy underworld looking for clues about the missing magistrate's son, then awesome! Its important to find out if your group wants story, or conflict and try to tailor fit the adventures to the group.
As the DM, this will be a view you will become accustomed to.
The DM has a very special job because they create all of the fun that the group has. Most specifically they role-play as all of the characters that the group interacts with. From the King, to the Evil Wizard to the scullery maid. Because of this role-playing interesting characters is important! (I'll do some posts about effective DM role-playing in future DM's Corners) As a DM its important to know the rules, be sure to carefully read over the rules for the game you're playing. If its your first time, explain to your group that you need their support and patience. As a general rule for a DM, if a result is very unclear but something could benefit the players, then take that course of action. Your plan for the game may be different but remember, killing all of the players off constantly may be fun for you, but its will quickly get irritating for the players.
In future posts I'll explain the basics of Campaign and Adventure creation, in addition to tips for the players as well!