I'll do the first with
Byzantium
(Monarch, Normal Speed, works with recent SVNs up to at least 614)
It is imperative, that you chose the 3000BC-scenario. It might take a few tries to get a decent starting position, but if you do, no one is going to stop you.
You start as the most advanced civ of your time (China usually being a close second) AND you get Greece including all its wonders!
Usually your starting position looks a bit like this:
Revolt to Theocracy and Warrior Code on the first turn. You can revert back to Mercenaries if you're playing for the UHV and fulfilled the first, but untill then you don't want to waste so much gold on unit support.
And you'll get Greece, Turkey, Jerusalem and a city in North Africa via flipping. Rome has never declared war on me, so having Persia alive is really awesome, since their declaration gives me 2 Cataphracts and 2 Horse Archers (that can immediately be upgraded to 2 more Cataphracts).
But what is far more important is the distribution of Wonders:
You'll want the Great Lighthouse, Great Cothon and Great Library in your Greek cities or Constantinople. Ideally the Temple of Artemis and maybe even more wonders (don't worry too much about the Colossus, you'll get it when conquering Rome if you don't start with it).
You also want either Persia alive or the Mausoleum already built (Rome might build it, but I usually don't want to risk playing without it and roll up a new start)
My current starting save looked like this:
(keep in mind that this is an almost perfect start, but anything even slightly resembling this is fine)
Athens:
The Lighthouse, the Colossus, the Temple of Artemis, FIVE settled GPs and a settled Great General, topped of by an Academy
Constantinoples:
The Great Cothon and the Great Library - yay, all useful wonders are here (also the Statue of Zeus, which could help if you get the Amphitheatre-quest)
I had other starts where the Greeks had founded Sparta with the Great Cothon (more than 15 workable water tiles!) or other combinations. Anyway: you want the 3 great wonders and then some as a start. Plus the possibility of the Mausoleum.
The initial phase (untill the Arabian spawn)
Cities that will later flip to the Arabs either build units (Cataphracts, Catapults, Workers) or directly wealth (I usually whip a spy or so just before the flip to bring the population down).
If like me you start at war with Persia, go for Babylon (flips to Arabs) and the cities north of it (flip to Ottomans) but make sure not to destabilize them to much. Make peace as soon as possible and gift them Calendar & Marble, so that they can build the Mausoleum. Since you'll experience at least 2-4 Golden Ages, this is really important.
Having Persia in your game also means you get to pillage all the nice cottaged tiles surrounding Babylon (this can give you up to 200 gold in total), which will slow the Arabs down a little and give you the cash-influx you need in the beginning.
Constantinople or Athens starts building the Apostolic Palace right away (with maybe a work boat or Hippodrome before that, if necessary). Since Athens had a settled General, I chose Constantinople.
You want to finish this building around/shortly after the Arabian start. Usually Rome will become the holy Orthodox city and get the shrine.
All other cities that dont flip, build walls (anything west and southwest of Constantinople) to defend against Arabs or Units (Cataphracts/Catapults)
I usually pump out a Settler in Jerusalem to found Ragusa (on the Copper on the Balkans, it is still in your core and gets a decent production and profits from the Lighthouse).
Diplomacy/Talking to other civs
Become friends with Ethiopia (they'll provide you with slaves) and try to get 1-2 units to the far east (usually by getting Persia to open their borders and then following the Silk Route, if you're unlucky you'll have to go through Siberia). China and India will provide you with Happy-Res that you'll need for UHV2 (make Constantinople the biggest city in the world).
Don't trade too much with Rome. If they have a tech they want to sell you, fine (usually you're their worst enemy untill the Arab spawn so they wont) but don't help them.
Research
If you're going for the UHV, you'll set your science-slider to 0, but with a start this great it would be a shame to waste it on the UHV.
So we research Meditation (usually you can buy this from Zara or Chandragupta, but I recommend researching it anyway since almost all later civs start without it and you'll be able to sell it to each of them this way).
My recommendation now is to start researching Civil Service and Paper but not finishing them (600AD-techcost-decrease!)
After 600AD first complete Civil Service, then Paper and then go for Education to get Gunpowder next. This path led me to Cuirassiers around 1030 so in time to upgrade my Cataphracts to Cuirassiers for the Seljuks.
Military preparations
After the potential initial struggle with Persia, make sure your border cities (Tyrus, Ankyra and if you own it Paraetonium in North Africa) have walls and a few defending Roman Legions, Archers, maybe a Cataphract and 1 Catapult each.
All other units should gather on the Balkans and prepare to march towards Rome.
Your declaration of war should come right after Arabia flips their cities in Egypt.
If you're lucky they won't even have Feudalism by the time you attack. (This is why you shouldn't trade with them).
Have your units march straight through their territory towards Rome, don't bother bombing down their defenses and sacrifice 1-3 catapults before taking the city with your Cataphracts. Take Pompeii too and raze Mediolanum.
Don't try to press the Arabs too much untill you hold Rome. If you start at peace with them you can even get open borders since you'll both be fighting Rome (take the deal!)
If you're at war, go for Babylon/Northern Turkey. You want to be able to reach Iran and India, either by conquering your path there or by getting open borders.
But try to make peace as soon as you have a way towards the east.
Constantinople builds infrastructure and wonders (for UHV2 - most cultured city) and just grows, while you can whip the rest of your cities to get basic infrastructure and more Cataphracts (you want as many of them as you can get, ideally at 10+ exp, so settle your first generals in your most productive city that is not Constantinople).
Build a spy and send him towards Malis spawn area (spy won't get attacked by barbs/animals)
Your army continues east and should conquer Persia next, they have lots of nice happy-res and the Mausoleum after all. If you already own a muslim city have 1 missionary spread it to Constantinople (and maybe Athens).
Now it depends on whether or not India collapses (if they do, conquer and set all later Mughal cities to produce wealth / 1 missionary of each faith, Mumbai to build infrastructure), build walls in your Iranian cities to fend of the Seljuks. (The missionaries are for the nice-to-have but non-essential wonders limited to these faiths. Also a confucian missionary from Samarkand might be nice)
It should be something like 900-950AD about now (earlier if you're lucky/really good, hopefully not later than 1000AD).
Now you have to decide what your goal is (Hindu, Orthodox, Catholic, Secular religious victory? Spacerace? Domination?...)
The Arabs will build the Spiral Minarett around this time, which is what we've been waiting for (also Mansa Musa spawns and if the Arabs haven't build it yet, then you should start else the Moors might finish it). Either wait for the Seljuks to soften up the Arabs a bit or (if it is in Egypt) go for their Egyptian cities.
The Seljuks will spawn in Iran in 1050 and then spawn stacks of units next to Babylon and Ankyra the following turns. Since you have walls in your cities, you have 2-3 turns before they would attack, which is enough time for your Cataphracts (or Cuirassiers) to finish them off.
After the Seljuks you should press the Arabs but beware, by 1150-1170 you should be able to sue for peace/finish them, since you'll need to heal your units for the Mongols. With your highly promoted Cuirassiers and a few bombards you should be able to defeat their stacks easily. After this collect all your units in Constantinople for the Ottomans.
They flip every unit outside a city in Turkey in 1280 and your cities including units stationed there in 1300, so station only 1 unit in Ankyra and the rest in Constantinople. Also don't worry about whipping Ankyra too much.
Try to keep an eye on the victory advisor since fulfilling UHV 2+3 nets you 12 turns of Golden Age, which is quite nice (you might have to sacrifice the Great Artist from Patronage). I kept on building wonders in Constantinople untill the end of my game. Important is building the Blue Mosque in Constantinople or your 2nd biggest city (Rome? Athens?) and the Opera House. This will help your domestic stability a lot. (if you have Paraetonium or another huge city in northern Africa it could be a good idea to build one of the 2 wonders there and settle all your Ethiopian slaves there for a huge production-boost at virtually no cost)
Since your Empire is quite big (population-wise) slavery is essential to stay under the population limit for the research penalty - and it is a good incentive to try to reach the industrial era soon, so that you can have 20 more people living in your cities before that penalty kicks in.
With this start I have won a Hindu URV and almost finished an Orthodox URV, with a similar one I did my Catholic URV, all sometime around 1400AD (I usually enjoy being so powerful and able to build so many cool wonders too much to finish earlier^^)
If you're going for the Orthodox URV, I recommend staying Catholic untill you start the reformation, converting (free shrine, yay!) and then switching to Orthodoxy (which you should start spreading from early on, so maybe from 1000AD onwards). For the Hindu URV I collected the 5 GPs and settled them before the Mughal spawn (you don't need to own the holy city for the URV, but you need it to settle the GP) and then switched to hinduism before I entered the Versailles-GoldenAge.
PS: I recommend building a fortress on the horse north of Constantinople ASAP and stationing a Legion and a Spearman of your initial stack there to defend against barbs from the North. After the Conquest of Rome you might want to station a Cataphract here as well, to catch the ones that go around your defense. They also help a lot in case a Mongolian Stack spawns there or the Mongols meant for Russia decide to attack you instead, so that Constantinople doesn't revolt.
PPS: If you plan on playing for a while after the Ottoman spawn (1500+) it might be a good idea to raze Ankyra after the Ottoman spawn (theoretically you could raze it after giving it to the arabs or seljuks but that doesn't seem that useful to me) and instead found 2 coastal cities in your Turkish Core
