Others have mentioned much of what I would say:
–in-game tutorial for the basics
–quick start option that limits number of initial choices
–a ‘Dominionspedia’ integrated in the game
But most of all I would think newbs would benefit by two or three deeper in-game tutorials that guide a player who knows the basics into the level of developing a nation-specific strategy.
Specifically what I envision are in-game versions of Bruce’s two essays in the Dom4 manual, “Bogarus: A Step-by-Step Strategy” and “Ulm: Crusaders of the Arcane.” These were very helpful, since they demonstrated, in a detailed manner, how you plan out a Pretender and a strategy based on the units and strengths of a particular nation.
Problem was, they started on page 118 of the manual, so many newbs never found them, and those who did had work through the discussion of real world historical analogies to the nations being discussed. While interesting, I think the academic style of these mini-strategy guides limited their effectiveness.
So I’d love to see something like that in Dom5, and for several nations. If these cannot be offered in-game, I would offer them as stand-alone pdfs, and eliminate academic tone. Make them only, “here’s how you develop a nation-specific strategy” and keep them separate from the manual.
With regards to a basic tutorial, the one in the Dom4 manual was 16 pages. If a tutorial could not be done in-game, I would create a separate pdf that is just the basic “let’s get started” and could be easily printed out.
I realize this is a game where you do really need to RTFBGM. But if you want to increase the player base of the game, recognize that many gamers in 2017 won’t. Offer them something that is built into the game, or at least a pamphlet rather than a tome to get them jumpstarted.