I didn't even read Session Minus-1 before I wrote this, so I hope it's not in a totally different format. But it probably is. Oh well, it's free and you get what you pay for!
YOUR FIRST ADVENTURE SESSION
So you have your people lined up and you meet for the first session. I will call it Session Zero because it happens before the proper campaign starts.
1. Have the people meet each other or if you have met before, have a little table conversation. Bust out the snacks.
2. Give them the elevator pitch for the campaign, whether they have heard it before or not. This will focus the next part of the event. It helps the players but it also helps you.
In my opinion the most important distinction between players is that some of them are content to tour your adventures and hang out and have fun, while other players want to direct the action and take some measure of control over their character's life and the world around him.
These are both perfectly appropriate strategies to have fun playing D&D.
There are many other ways to divide up groups of players or recognize distinctions, but to me this is the most important one.
3. Invite everyone to help decide what kind of campaign they want. See if everyone can agree if they haven't before. At this point you can start to get a feeling about which players will be more active and self-directed.
4. Then everyone can talk about the races and classes they want to play and figure out how to get the bases covered. Once you all know what the thrust of the adventures will be about, it will be easier to know what kinds of characters will be most useful.
5. Depending on the system you are using, character creation can take ten minutes or two hours. Not everyone has a book. Not everyone can settle on one idea or another. Do it together and support each other. Make sure the players who get done faster are engaged with the players who are a little more methodical.
6. One specific thing I am going to try to do going forward is insist that the players establish that each character knows at least one other character and the nature of that relationship, such that every character is at least an acquaintance-of-an-acquaintance of each other one. Consider it a string of connections in a way that connects them all even if any particular one is once or twice removed from another particular one.
7. At the tail end of the character creation, do hirelings and pets if they want to. Give them a chance to do shopping.
8. Then do a little five-room dungeon so they can get the first taste of working in a group and fighting and finding treasure. I do a little temple with a patrol, a straight fight, a clue, a puzzle a boss fight, and a bonus fight for better treasure if they figure out the clues and puzzles. Every time I run it for new people it goes a little different so I stay engaged as well.
9. Then after that tell them hooks. Rumors or someone running in with a message or a bulletin board in the middle of town where people post bills to each other.
Then you're done with the adventure for the night.
10. Then make them well aware that email and texting are not required but very welcome. There are in-game elements that can and will happen that can be handled away from the table. Technology is awesome for making more table time magically appear when you least expect it.