It's good to play through the normal core campaigns before tackling the custom ones. If you do wish to try some of the "Very Hard" custom campaigns later, then my best advice is for you to learn the micromanaging skills NOW, while you play through campaigns of lesser difficulty.
"Micromanaging" in Emperor means using skills and tricks that allow very rapid immigration, population increase, food production, and housing evolution. You might ask: why bother doing these things so fast? The answer is that in many of the custom campaigns there are time limits set on the missions, so you must play the game at an increased pace to win the missions within the time limits.
There are many micromanaging skills but in my opinion the most vital ones to master are how to juggle the immigration and worker distribution in the FIRST game year to pull in a harvests of food and hemp in that FIRST game year. If you can do that, your city is poised to hyper-evolve and things become much easier.
Perhaps the second most important micromanaging skill is how to build cities with "perfect harmony" Feng Shui. The game provides many hidden bonuses if you have perfect harmony Feng Shui in your city. These bonuses are very powerful - yet often overlooked by players, who are unwilling to take the time to hunt for the "green" footprints (which denote perfect Feng Shui placement) for every building they want to put on the map.
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[This message has been edited by Gweilo (edited 05-10-2020 @ 01:42 PM).]