To welcome a new user I would definitely tell about the projects that supports and help newbies and minnows. A great projects that isn't mentioned before is:
Minnows Accelerator Project

I would also explane that upvotes are not the same as likes on Facebook! I believed that my first time on Steemit and had no understanding about the limits of SP.

It's also important to tell new user that this is not like Instagram. I posted several single photos during my first time. That will not bring much attention. Many people work hard to create great content and that is the way to go:)

I would defenitely tell a new user about the importance of being a nice person and to get to know as many other Steemians as possible. Through the projects but also by reading posts and writing kind and supportive comments. The communication is very important if you like to succeed on Steemit.

There is also nice to go through the interface with new users. Where do you find replies to your posts and comments? How to handle the wallet? I would tell about the importance to keep the active key or password safe.

It would also be a great idea to provide a list of markdown code, this was really a struggle for me to understand on my own.