We inherit the game in 1AD with seven cities, but no workers built - and we are only allowed to build workers in cities of at least size 6 (which none of our cities are)! We don't have Currency yet and have no cottages, but a lot of regular warriors and archers "protecting" our cities, which results in a really bad economy even at 0% research. So let's have a look what I can do! Here's our starting empire, as we were shown before the game:
First order of business was to make sure that as many cities as possible would reach size 6 as fast as possible, so that I can produce much needed workers. Every city got set to emphasize food except Salamanca, which was optimized for max hammers to finish the obelisk faster, to get the cow in range. Every city started to build a granary, then a library. I also notice we're paying unit upkeep, so I disband all warriors and even some of the archers so that I will be able to have at least some workers without having to pay for them. In case I get attacked, I can quickly produce new ones if needed.
To avoid being attacked in the first place, good relations are key. I notice that we have no open border agreement with Qin, so I sign one. I also do not convert to any religion - diplomatically, it's better to have some cautious relationships, than to have some pleased and some annoyed. Also, AIs in CIV are kind of tame anyway, and at Prince difficulty even more so, so I don't think I'll get in trouble unless I want to.
The last big question before hitting "end turn" for the first time is what to research. We lack even basic worker techs like Mining and Bronze Working (and that with having access to a gold resource!), so that would be an option. We could also research Mathematics and Currency to help our economy. But instead, I do what I like best: I set research to Alphabet. Alphabet is one of those techs the AIs tend to ignore for a long time and which enables tech trading, so with a little bit of luck I can use the tech to trade my way out of this hole! Additionally, it lies on the path to Literature and the Great Library, so maybe I can get this powerful wonder as well.
I need Alphabet as fast as possible though, before the AIs get to it, so I decide to burn the 109 gold pieces we started with, and set research to maximum for a few turns until I'm completely broke.
With no units to move, turns fly by quickly. In 75AD, Seville reaches size 6 and is immediately set to produce workers. Lots of workers! Barcelona starts to do the same in 150AD, and Cordoba in 175AD. When Madrid reached size 6 in 200AD though, it does not build workers too, but instead continues to build a granary and a library. With its commerce bonus for being a capital and lots of cottage potential once I would have workers, the bonus research from having a library would be maximized. Additionally, I wanted to hire scientists to get a great scientist as fast as possible, and the library is a prerequisite for building the Great Library, so I felt the move of not producing workers in Madrid is justified.
In 225AD, Seville produces our first worker! He immediately starts to construct a cottage on the floodplains tile the city was working. More workers were produced during the next turns, and they started to connect resources and construct cottages. I carefully paid attention to construct cottages only on tiles the cities were working anyway while producing more workers, and also concentrated to build cottages at Madrid mainly.
My plan to rely on the AIs not to research Alphabet suffered a first setback in 350AD though, when suddenly Caesar knew the tech. This was a blessing in disguise though, as he did not know Monarchy yet, and I could trade it to him!
I was tempted to trade for Mining instead of Mathematics, but Mathematics gave me more beakers overall. Additionally, I expected to trade a lot in this game, and feared to hit the dreaded "We Fear You're Becoming Too Advanced" cap too early, so I decided to research Mining later myself. I still find it a bit silly that the WFYABRA cap is based on number of techs instead of number of beakers!
My workers did not waste time to build roads and focused on improving my economy instead. However, Saladin had a city in the far north of me, and his workers conveniently built a road through my territory - thanks mate!
Another reason for me to prioritize improving my resources besides the extra food/hammers they gave was that I was eager to trade them away as soon as I could. The first opportunity to do so came in 500AD, when I sold a rice resource to Hatshepsut for 3gpt (she and some other AIs apparently knew Currency already).
This is not a deal I'd make normally, but in this case I was willing to pay through the nose to get additional gold per turn. Everything to get Alphabet and trading possibilities sooner! In the same vein, I sold Qin my only horses for 3gpt in 540AD, and would make and renegotiate more of these deals later. In 640AD, Saladin knew Alphabet too, so it looked like I could lose this race...but no more AIs got the tech until 760AD, when I finally discovered it. I did not trade it away immediately though, but waited for one extra turn in which I researched Mining. Then, I finally did what I can do best: Tech trading!
Alphabet went to Elizabeth for Bronze Working, Monotheism, and 90 gold. Then, for Alphabet, Polytheism and 80 gold Qin was willing to give me Currency, which alone did wonders for my economy! Some turns later I sold Qin Monotheism for 170 gold, and my research speed was finally acceptable again.
I researched Literature next, to build the Great Library, and also stopped producing more workers at this point. I had 14 workers now for 7 cities; a lot more than I would have in normal games. I needed these workers not only for constructing more cottages, but later also for chopping forests to speed up the construction of the Great Library in Madrid, as a lot of AIs had Literature around the time I discovered it.
But first, Saladin came knocking at my door to demand I should convert to his state religion.
I took advantage of our spiritual trait, and caved in to his demand. Everything to keep the AIs happy! This way, I got a +1 diplo bonus with Saladin, and converted back to "no state religion" 5 turns later.
After Literature, I wanted to have Civil Service as fast as possible, both for the Bureaucracy civic and for its excellent trade value, so I researched Code of Laws next. I still lacked Metal Casting, Construction, Calendar, Feudalism and Iron Working, but I saw no use in researching techs the AI knew already. This proved to be a wise decision, as when I discovered Code of Laws in 900AD, I was able to trade it away for Calendar, Construction, and Iron Working.
I also monitored the resource market closely, and when Hatty suddenly had an extra gems to spare in 920AD, I traded away my only gold resource for her gems. Why that? Both resources are of equal value (2 happy faces with forges)! But I knew I would have a second gold resource soon, once borders at Salamanca would expand another time:
You have to plan way ahead if you not only want to climb out of a tech hole, but also want to take the lead...
In 1000AD, I completed the Great Library in Madrid. In addition to the 8 great scientist points the wonder produced, I hired two extra scientists there to speed up the generation of my first great person. I was still concentrating on improving my economy and research speed and ignored military completely, so when Caesar made another deman, I felt I had to cave in again to keep the AIs happy.
The turning point came in 1060AD, when I discovered Civil Service and switched to Bureaucracy. Here's my capital after the switch - note the +14 GPP which just had produced my first great scientist, which I used to construct an academy.
All my efforts to strengthen the economy now allowed me to do 70% research at break-even cost, which was very nice.
Research was set to what I always seem to research after CS: Paper, Education, then Philosophy and Liberalism. This Path (Civil Service - Paper - Education - Philosophy - Liberalism) is a very powerful one, as it gives you access to a lot of powerful civics (Bureaucracy, Free Speech, and Free Religion) which will boost your research rate considerably. It also gives you access to Universities and the Oxford University, which provide yet another research boost. And on top of all that, the AIs ignore these techs for a long time, which a) accelerates your research speed relative to theirs even more, and b) allows you to easily trade for all techs you have ignored on the way. This beeline is so powerful, overpowered even, that I almost never see a reason not to follow it - which makes it kind of boring, to be honest.
So after I've been the only one to enjoy Bureaucracy for some time, I decided to trade for the techs I missed. Paper went to Saladin for Metal Casting and 140 gold. Civil Service was given to Elizabeth for Feudalism and 30 gold. Hatty received Paper for Compass, her world map, and 40 gold. And Civil Service and Compass yielded me Machinery and some gold from Caesar, and Paper and Literature were enough to get me Optics and 40 gold from Qin. I really think that trading is the key to master this game!
But at least equally important is to know when not to trade. Saladin was the most dangerous AI at the moment, with the largest empire and the biggest science output, so I took care not to trade him Civil Service.
Now that I had a clear tech lead, victory was secured - after all, this was Prince difficulty level only. Normally, my usual path would have been to get Astronomy next as the free tech from Liberalism, to speed up my research even more, and to cruise to an easy victory, either via space race, or by having fun with macemen, riflemen or tanks. But that would be boring to do again! This was an unscored event after all, so I decided to do something I've had on my list of things to try out: Having fun with cannons.
My normal research path has the consequence that once I have access to cannons, they are more or less obsolete already and/or I have access to artillery. So when I was only one turn away from Liberalism in 1240AD and the AIs still lacked Education and Philosophy, I decided to postpone the discovery of Liberalism and instead to research as many prerequisit techs to Steel as possible. While doing this, I finally met Mansa Musa; I hadn't noticed there was still an AI missing... But since he also lacked Education, I continued to research the prerequisits before I finally finished my research on Liberalism in 1430AD.
I switched civics immediately to Vassalage and started to produce an army. Let's have a look how powerful early cannons can be! My first target was obvious: Saladin, who was my direct neighbour, and who posed the biggest threat to me. The war would cancel some luxury deals I had with him, but fate decided to help me with my plans, and I "popped another one" at Cordoba one turn before declaring war.
While preparing for war, Saladin had already attacked Hatty - nice, maybe he would lose parts of the really large army he usually has. Unfortunately, Mansa Musa used a great engineer to finish the Taj Mahal some turns before I was able to build it, so I had no golden age to help me in my preparations. I declared war on Saladin in 1555AD; here's a screenshot of my empire from that date.
It was also very unusual for me to produce grenadiers - another unit that is rendered useless by my usual research path. I had skipped a lot of techs on my way to Steel, too - but would trade for them after the war.
I could feel it - fun turns laid ahead of me!