Disclaimer: I have little experience (but not no experience) running tabletop games, but I have tons of experience hosting, organizing groups and playing. My advice for starting out:
Know your hook (or hooks) but don't force your adventurers to follow them. Let the adventurers guide you instead of the other way around. You don't want a campaign to be like a puzzle that they have to figure out. That makes it more like a board game, with a specific end point that they are supposed to work for. It's much more fulfilling (for you as well as the group) to allow them to shape the story itself with their actions. Could they waste a couple of sessions chasing a false lead only to finally figure out they were going in the wrong direction? Maybe. But Something Else could happen because of where they're focusing their attention, which could bring them back to the main storyline, or to make a storyline out of what they're doing that you hadn't anticipated.
A lot of this can be made up on the spot. You probably should have reference sheets or bookmarks for the stats on the majority of the creatures and important items that exist in your world so that you don't have to pull them out of your ass (or waste time looking them up every time you need them), but you don't have to specify exactly how many of each creature are in each place ahead of time. Remember that your players may mature and progress at a different speed than you have designed your campaign around, and you may have to be flexible with some things. Don't be afraid for them to fail, but party wipes are super demoralizing and it's hard to justify bringing them back when they all die.
Also, don't let your players keep their DMG's or Monster Manuals near them. You determine the rules in your games, not the other way around. You need materials for reference but you are not bound by what they say. One of my friends is really adept at making up creatures - which you can do, too. If you need, say, a pumpkin-headed plant monster, you could find a mob with what you think are appropriate stats for it and use them with the outward description of your monster instead of the monster they belong to. Along the same lines, you don't have to use the template for the stats of every creature of that type. If the party comes upon a group of bugbears, for example, they don't all have to have +5 morningstars, 16 HP, 5 foot reach, be chaotic evil or have the same ability stats.
I would recommend running a short premade campaign to get the newbies used to the game before they jump into a campaign that you have put a lot of thought into. I'd make it at least 4 sessions long and pre-plan the gaming nights. You don't want a couple of your players realizing that they don't enjoy it and dropping out after you've already started them through something that you personally created for them, or to start into the campaign only to realize that some of your players are frequently absent, late, or super fucking annoying.
Figure out where you're going to play and what the setting is going to be like. Will people bring food? Can people smoke there? Will there be drinking? How long will the sessions last? Is it kid friendly? How often will you meet? What happens if someone misses a night? Everyone needs to agree and know what to expect from the sessions ahead of time.
Work on assertiveness. You will need to be able to keep these people on task without seeming like a dick. Any time you get a group of non-gamers together and try to get them to play a game, it's going to be hard. You will need to be very comfortable with helping people build characters and understand the concepts so they don't feel confused and lost and end up not enjoying themselves, not paying attention or dropping out. Don't expect them to catch on as quickly as you could. Some people are dumb.
Hmm, I guess that's enough for now.
