Note that this thread is not intended to be a "wish" thread. I don't want to see dozen of posts like "I want tutorial how to add super-extra-cool ship with mega-blast weapons and a lot of cash".
Instead I would like to see posts like "I already wrote tutorial xy"

Who should write the tutorials
Anybody who thinks he know how to do the particular thing. Please don't think like "there are better then me...". There is always someone better then you. That doesn't mean you cannot tell others how to do that. The worst thing that can happen to you is that you will have to correct your post

So here is the list:
How modding works in a first place
What is modding, what can be changed by modding. Difference between modding and scripting.
How to unpack your game
How to unpack your game with X3 ModManager
How to create a mod (catalog)
How to ceate a mod using X3 ModManager - this is just a very spare tutorial imho. Better then nothing though

How to add gun to a ship
This will have to wait until DBOX will be released. How to modify ship scene file and to update TShips accordingly. You may write down how to do this manually (possibly using notepad?) if you want.
How to add/change names of objects (sectors, ships, lasers)
How to add new strings into xml's, how to manage the xml files properly.
How to add a ship to TShips
This is not so important imho but it would be nice to tell people how to do that. What are the "critical" (important) values in TShips.
I think that these are the most critical tutorials. If you think that some are missing, write them down.