Sid Meier's Civilization IV

City Founding & Early Game

• A well-balanced early game city location has at least a couple of resources, enough food for growth (at least some grassland), 2+ hills to build mines on, and is located next to a source of fresh water which increases city health and is required to build farms early on.

• A new city's top building priority should be a source of culture, usually a Monument, to allow its borders to grow. Granaries are also an early priority as they allow their population to grow much faster.

• When exploring the map, focus on the nearby areas first for potential city sites. Also, stick to forests and hills to have better odds against roaming animals and barbarians.

• Barbarian units only spawn on tiles no one has visibility on, so keeping a few lookouts outside your borders can help reduce their raids.

• Get Archery and a couple of Archers for each city sooner rather than later, as barbarian Axemen can easily chop up basic Warriors. Cities built on hills are also easier to defend.

• Make new cities whenever your economy can take it and there are even slightly worthwhile locations nearby. You don't have to maintain 100% research at all times, though try to avoid dropping too low unless you know it's only temporary.

City Management

• Regardless of how much a city's cultural borders expand, city pops can only ever directly collect food/hammers/commerce within the 2-tile radius around the city. Resources can be collected from anywhere within your borders.

• Familiarize yourself with the small buttons in the bottom right of the City Screen. They allow you to change your city's focus as needed or automate its functions which is very handy in the lategame.

• Specialize your cities. Have one with the intention of pumping out great people, a couple for commerce and a couple for production.

• The more cities you have and the further they are from your capital the more they cost to maintain. Building Courthouses and the Forbidden Palace national wonder or adopting the State Property civic are ways to reduce maintenance.

• Make sure to connect all your cities to your city network. Cities connected to each other and/or other civilizations' cities establish Trade Routes with each other (visible in the left side of the City Screen) which increases your income. Rivers and later coastlines can also serve as connections.

• Removing all forests around a city may seem tempting early on, but it's a good idea to save some for later. Once you get access to lumbermills, they become very productive.

• Don't neglect building Cottages, they are weak at first but become quite lucrative over time. Keep them safe from enemy units though.

Military & Warfare

• Attacking and defeating a unit usually gives more experience than defending against one. If the odds are strongly enough in your favor, don't be too scared to go on the offensive.

• On a larger scale attacking a city is usually costlier than defending one, so only declare war if you're clearly ahead of your target in either numbers or military technology.

• Don't neglect your military. The AI can smell weakness and will attack you if you don't have a lot of troops, even if you are relatively friendly. Try to keep at least one city pumping out units.

• Taking cities becomes much easier with siege weapons, starting from Catapults. Aside from reducing city defenses, siege weapons can be used to attack enemy stacks directly, dealing large amounts of "collateral damage" to multiple units and making them easier targets for your main combat units.

• You can pillage enemy improvements to hinder them and to make some extra gold, though be careful as this uses up the unit's action.

Diplomacy & AI

• The Info Screen (F9) allows you to get a rough idea of other civilizations' military power, amongst other things. Keep an eye on it to know who's weak and who's strong.

• Use religions to form power blocks and don't be afraid of changing yours if it suits the environment. If you have strong and aggressive neighbors, following the same religion as them can be a matter of life and death.

• Sometimes it's worth making friends - not just to prevent war, but to open the possibility of less successful neighbouring civilisations offering to become vassals.

• You can turn off technology trading in Custom Game to prevent the AIs from trading all their techs with each other.

Miscellaneous

• Multiple Workers in a stack multiply the speed at which they complete improvements.

• Slavery is a very powerful civic if used correctly, sacrificing a pop or two can sometimes be well worth it, especially if your city's already at its happiness cap.

• Don't get wonder-blindness, consider if you really need one as they're not all worth the time and effort.

• Use your cultural borders to your advantage. Rush to grab areas of land cutting off enemy expansion and using oceans/mountains to create strong defensive areas.

• Your strategy should change based on what kind of map you play. Adapt your tech choices and what you're focusing on to your map type and starting environment.

• Try to diversify your resources, in particular sources of food and luxury items. Each is effectively available in unlimited quantities, so your entire empire will benefit from their effects. This does require you to connect all your cities to your global trade network, so be sure to build roads between them as early as possible!

• Being the first to sail around the world gives all your ships a nice +1 movement bonus. If nobody's beaten you to the punch yet, build a Caravel and send it in a horizontal line to the other side of the screen. Better yet, build two and make them go in opposite directions.