Also here's the advice of someone who could not succeed on King until he understood the importance of these two things.
TRADE-its super important, ask anyone who plays at king or above, money buys happines. When you begin playing king you start having serouis problems with unhappiness, the easiest way to quell that is to set you lux rate at about 30%. You never had too on prince because it was prince. Try sending out about 20 to 30 profitable caravns to increase trade, build all the roads you can, and make tax collectors. If you do all of this successfully you should improve part of your game.
The other important thing to remember is to expand. there are many forums in here that talk about the importance of expansion(go find them) they talk about the super-expansion technique(which is also is Tszu Tzu's <-
war acedemy) and all kinds of stuff. If you want to know how to get over 20 cities before 500BC go there.
Expansion is IMPORTANT you have to learn how to do it to be successfull!!!
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"It is well that war is so terrible-we should grow too fond of it."
-Gen. Robert E. Lee, 1863