Civ4 Trade Deficit

[BlackOmne]

I have nearly mastered every bit of the game, except for trading. I can usually arrange to get my civ the number 1 ranking in the demographics screen in nearly every category except for the Imports/Exports category, where my civ is usually close to last.
I'm guessing that I'm making bad trades (eg, either trading a rich resource for a poor one or not getting sufficient monetary value for a resource). But, there doesn't seem to be any indication of the precise value of a resource, other than a general expectation that gold is more valuable than something like sheep.
Is there an easy way to tell what the precise value of a resource is that I'm missing?

[EpicLord]

Well in general:

Military > Happiness > Health

With military being far and away having the highest value.

[iru]

The Imports/Exports category doesn't care about your trading decisions but about the value your trade routes brings you compared to the value the same trade routes brings to your trading partner. The value of trade routes are based on the foreign city meaning that a low Imports/Exports value tells you that your cities are better developed than the AI's.

The easiest way to get better Imports/Exports values is to build harbours in coastal cities. When the game calculates trade routes a city with harbour built is twice as attractive. (Meaning that your 6 population city might gain a trade route with a 10 pop AI town and thus you earn more than the AI from the trade route)

The Demographics screen explained:
http://www.civfanatics.com/civ4/strategy/demographics.php

Math relevant to trade routes:
http://forums.civfanatics.com/showthread.php?t=159047