Don't watch frog play on you tube he makes very bad mistakes and he covers nothing on city building and kindgom expansion.  Sometimes I believe he makes the mistakes he does playing on you tube just to make the AI look better.  I am not saying this is true, but this game is not hard to beat and out play the competition even on ridiculous / ridiculous settings.

This is what I did to learn how to play at release.  Realize your mistakes that you did from the prior game and read the descriptions of all buildings.  Have a planned route up the tech trees.  If you do not know what is on the tech trees look through them before just picking one and make sure they compliment your gameplay or strategy.

You need to learn what to build, when to build and what to study in both the tech tree and magic.  Magic is easy because basically you only need a very few spells for the entire game.  Actually 2 spells, but I dont want to get started on the lack of magic thing.

Once you got this down you will be able to play on rid / rid with no problems and win every single time with your eyes closed.  Well one eye open for roving monsters, but the factions will fall fast with no difficulty.

As a side note I have never played the campaign, but from what I have seen others say it has nothing to do with the sandbox version.