[Based on the fact that this is a mobile game development blog, this is a little off topic. But, let's admit up front that my greatest love of gaming is in storytelling, which is born from pen and paper games. So, that translates directly into the creation and design of story, plot, and characters within our mobile games. It may seem a digression, but actually its right on topic!]
In answer to a friend who asked, "Do you have any recommendations on how to be a gm?"
After some thinking about it, I came up with a few thoughts. This is far from comprehensive, and really tries to address my friend's direct questions.
Build the Story First -- Worry about the Characters Later
How do you get started? How do you make sure the story hangs together? How do you make sure you can keep the characters in the path without railroading them?
Our friend's exact quote was, "I'll never be as organized as Cory." Which is true. You aren't likely to find a game master who is so copious in preparation and organization as Cory.
My recommendation is to build the story first, and worry about the character's part in it later. It is too easy to start by thinking what the characters will see, what scenes they will move through, and how you manipulate them to keep them on the path that you have created. This quickly leads to trouble in a gaming session, because players hate paths, and are predictable only in being unpredictable, mad-house, and likely to kill your friendly NPCs to boot.
So, I would advocate to try to build your story the other way around. Scrub your mind clean of the player experience, and build the story, its actors, the world around it first. What is happening? Who are the big players, and what is at stake for them? What are the forces working against each other, the tensions boiling? Get a big idea and start to work out why its cool, dangerous, edgy, and how there are going to be winners and losers. Then work your way into the details a bit more, who are the actors, their underlings, and what are the street-level steps that are being taken to resolve this conflict?
If you start at the top and work your way down, you will eventually find an exciting place to insert your characters. But the real value in this exercise is later, when things start to get messy. If you have prepared from the bottom up (what the characters will see and do), as soon as they move outside of that path, you are struggling to find details, understand how the NPCs should react, and stuck trying to get them back on the path. If instead, you build from the top-down, you already understand the actors, their motivations, and the details that surround the whole situation. Therefore, if your players suddenly take a right turn and decides to back-stab their main contact, you have a depth of knowledge about the bigger landscape, how that might effect the bigger story, the other actors who might sweep in, and the potential consequences.
Build the big story in your head first, and understand it. You will also find that as a storyteller, you are called on to do a lot of improvising in any situation. If you can see the larger story and its players, this will always be easier, because your mind can pull details quickly from this larger context, instead of having to create them from nothing on the spot.
Storytelling is like Writing -- and they say, "Write what you know"
The friend was asking specifically about Shadow Run 3, and mentioned that he wanted to exclude hackers from the group because the rules are very complex and he is not familiar with them. I think this is a sage decision. Gaming systems are big and complicated, and you may not learn everything at once. Especially if you are kicking off a first game, work with your players to make sure they are happy with their character types, but it is okay to limit them to areas where you feel confident and know that you can adjudicate the rules fairly. Later, after you have gotten your feet wet, give hacking a try (for example).
It would be awesome if other players / storytellers want to post additional advice for new GMs!