Economics for Established Empires

No matter what your goal in Lords the key to it is money. Money lets you build your troops, your AQRs, your religious stats, etc. Even the strongest position will crumble for lack of adequate funds to maintain its military and government as well as expand to face future threats. In short, at its basis Lords is a game where economics is the key to power. Too many new players think that to achieve this goal they need a large empire. This is not so. Developing economic growth requires territorial basis that most players can achieve. Large empires are not necessary. Starting with five or six regions, preferably friendly and cultivated, that allow you access to several potential trading partners you can build yourself into an economic powerhouse. Once there any other goal becomes very easy to achieve. The key to economics is trade. The key to trade is cities.
Many players will tell you that the most cost efficient investment is Regional Public Works bought through NFP. In most games this is a ration of 5 NFP to one Public works. As Regional Public Works gives you 1 gold back (a 5/1 NFP/Gold ratio) and slightly increases your NFP pool it is one of the best investments for a small country. However, once you have reached a stage where you have several trading partners Cities will make you far more gold.
For example take an Empire with a Trade Value of 10 and an NMV of 0.18. Let us assume that the country has several level 4 port cities and the next break point on Trade value is a level 7 city. The cost to raise a city from level 4 to level 7 is 45 gold and 30 NFP (assuming the city is in a cultivated region). This has the effect of giving the country 3 gold through increased City Value, 3 gold through Inter-City trade and increases your trade value from 10 to 11. This increase in trade value will directly increase the gold you receive from trade by 10%. So, if said country was making 100 gold per turn through trade that would go to 110 gold. The effect of this increase in city value is 16 gold a turn giving you a ratio of 2.8/1 gold to build to revenue generated and 1.9/1 NFP to gold generated. As you can see this is a far more efficient ratio than the 5/1 generated by spending NFP alone on Regional Public Works.
This process gets even more cost efficient as a country grows. If a country with a trade value of 30 making 450 gold a turn through trade increases a city from level 4 to level 7 they generate 6 gold from City and Inter-City Trade plus increases his trade value by 3.3%, which translates in to 15 gold, for a total increase of 21 gold a turn. Thus the ratio of gold spent to gold generated per turn drops to 2.1/1.
Getting to the point where this process starts to be useful does take time but it is time well spent. To start with, once you have your territory established, your first goal should be to build a level one city in each province starting with your cultivated ones. This is the fastest way to bring up your trade value as well as building your city and inter-city trade incomes. Begin with the cultivated provinces where you can build port cities. As you are building these cities establish trade with everyone that you can.
Once you have all of these cities built, you want to start adding to them in a vertical manner. In other words you want to build as many levels as it takes to reach the next trade value break point to an individual city as you can in one turn. Remember, even though only one level of the city will be constructed in a turn, you can pay for several levels of building at one time. This process has two effects. First, it makes your wall building much less expensive as walls are half cost to rebuild on the turn that you expand the city and they do not need to be rebuild as it develops. The second is that in the long term it allows you to sustain your economic growth through tough times.
If for example, you are hit by a plague or a famine, or you need to divert money into your military, your city growth is already paid for and will not be effected. The next turn pick a different city repeat the process. So, if you have three level one cities, and the next break point for increasing your trade value is a level four city, you would start by building one of the cities to level four (or as close as you can get in one turn) and then move on to the next until all of them have been increased in this manner.
Once your port cities have reached a level where they can handle multiple fleets you should consider building internal trade fleets. Each Internal Trade Fleet will advance your Trade value and your city and inter-city income and may be cheaper than expanding your port cities to the next trade value break point. The also immediately increase these values where as increasing the city size may take several turns. One thing to remember, though, is that you have to have your cities developed enough to handle multiple fleets as Internal Trade Fleets are a support, not a substitute for, External Trade.
While this process is going on you should concentrate your extra moneys into building regional public works. Not only does this give you gold back, but it also increases your NFP, which, in turn, increases the number of city levels you can build. This, of course, increases your trade value, and gives you more gold to build more cities and more public works. It is a beautiful self feeding cycle.
Hopefully, you will find this a simple enough process. If you build up your trade income through development of your cities and public works you will find that all of your other goals are that much easier. After all, you can't build the armies you want till you can pay for them.