A huge different of civ 4 from civ 3 is that road doesn't add 1 gold to a tile. So more people don't necessarily mean more gold. Actually, most tiles are bound to generate no gold, -- unless you build a cottage. If you want to build cottage in some tile, you'd better do it as early as possible, because it takes many turns to grow to town. Cottage can be built in every workable tile, and it will grow ONLY when it's being worked. Now the question is: where to build cottage? Everywhere? Floodplain? Grassland? Plain? Hill? Chop forest? This question is more important for financial leaders, because a cottage near river immediately gives 3 gold.