Whoa, slow down.
Before you start to create your D&D campaign there are a few factors you need to think about. Including:
- Who your players are going to be?
- How many players there are going to be?
- What do your players want to play ?
- Are you playing Online or In person?
These Factors should be considered before you start to create your campaign as they have a huge effect on whether your campaign will be a success, or a complete flop.
The Point of playing D&D is to have fun, and as a Game Master your goal is to make sure that all your players have a great time. For that reason you should ask your players what type of campaign they would like to play, do they want a gritty or lighthearted game, do they want an epic story spanning thousands of sessions, or do they want episodic stand-alone adventures. Ask your players what they want and let their feedback inspire your decisions, about the campaign, because, after all if your players are not enjoying the game you are failing as a GM.
You should also consider how many players will be in your game, as you may need to make adjustments to your ideas to accommodate less or more players.
As a Noob GM your familiarity with the game may vary wildly. If you have been playing D&D for years you will be quite familiar with the rules. However if you are new to the Hobby, yet still want to be a GM, your knowledge of the rules may be lacking and this could make it very difficult when you eventually run your game. So how well do you need to understand the rules, well it depends on 2 major factors, whether you are playing online or in person and how experienced your players are at D&D.
If you are playing around a table, in real life, it will be much easier to adjudicate any arguments over the rules of the game, as all of the players will be able consult the rule-book (probably a copy of the Players Handbook), but, if you are playing online, squabbling over the rules could seriously slow the game down, it would also be harder for you to reign in your players and resume the actual game. If you are going to play online then, you must have an even stronger understanding of the rules.
Similarly, if you are running your game for inexperienced players, you have to be 100% confident in your knowledge of how the game works, so that you can provide help, when they eventually ask for it.
Conclusion
To sum it all up then, before you charge off to start writing your own D&D campaign, you need to know, Who you are playing with, what they like and, how you are going to play with them. Once you know this, grab a pen or get on a computer and prepare to write lots and lots of notes (a.k.a the fun part).
D&D for Noob Game Masters 