My advice would be to take it easy the first time. Make it as simple as possible.
Try using a premade module there are a number available on the internet for free if you look around. Read it first, cover to cover, so you know what is coming up and won't be surprised.
If you're not going to use a premade module, don't be afraid of cliche adventures. You may want to steer clear of them in the future, but as a first game, a cliche works wonderfully. An example of an easy cliche adventure: A local noblewoman is kidnapped by some bandits/orcs/goblins/etc .... that are demanding ransom in exchange for the woman. Her husband/father/barber hires the PCs to go into their lair and rescue her.
Try to use simple creatures. Monsters with complex rules will just slow you down early on.
Don't try to 'buy' the happiness of the players by giving out too much treasure too quickly. Follow the DMG guidelines on treasure. If you give them too much stuff too quickly, they get bored at higher levels when there is nothing else for them to get that is an improvement on their current gear.
Run the combats in advance by using mock characters and playing with yourself. No, not like that. A trial run through the module by yourself will help point out the pitfalls and problems. I wouldn't recommend doing this before every adventure, but I would recommend doing it the first time to get yourself comfortable with running a session.
Finally, don't stress about it. If things don't turn out as planned, just go with the flow and adjust as needed. As long as you don't get stressed out and you are having fun, the game will probably turn out just fine.