I guess this depends on the type of win you're looking for. Despot rush is very effective on any level. Build a couple cities, build barracks, maybe a temple and then TONS of units. Nothing but. Pop rush them at every opportunity. Rush everyone and win by conquest/domination. Another is old ICS. Very effective, and combined w/ despot rush and pop rush, just devastating. Build lots of small cities 2-3 tiles apart, overwhelm AI w/ pop rushing madness from multiple tiny cities. These are all fine and legit strategies and a lot of people like to play this way and they rack up huge point wins doing so.
But I want to win at these levels playing in the spirit of the game. Me, I'm more of a "purist" and don't like despot rush or ICS type strategies. Maybe I think it's too "exploitative", maybe I'm a romantic player at heart who wants to build an empire and culture and get wrapped up in my little world, not just rack up points by mindlessly cranking out units. Either way, I'm interested in strategies to win at Emp and Deity doing it "normally".
One way or another, it WILL involve early warfare. I don't see anyway around it. I think you'll have to incorporate at least SOME Despot Rush and pop rush techniques, though I find the "pure" form of it distasteful myself.
I'm playing Emp games now and have had "non rush/ICS" victories using the basic outline below. I plan on using the same when I start playing Deity (still working my way up to it) though I don't know yet what I'll need change.
Ancient Times
Standard expansion - build settlers ASAP, blah, blah
Exploration - send out scout/warrior and find all those near you
Science - set it 0-10%, forget trying to keep up w/ AI. rake in cash and buy tech from them
Diplomacy - trade, trade, trade tech w/ AI. Buy when you have nothing to give. Work diplomacy constantly.
Pop Rushing - I'll do it 2-3 times a city, no more or unhappiness will be a problem for too long.
Resources - get iron working ASAP, locate all iron near you and settle it. Find that lux patch near you and claim it. Rush like hell those who have it if you can't get it. You're dead w/o it.
Denial of Resources - VERY important on Emp, surely for Deity as well. If you can make sure at least one other civ can't get iron, you'll have no problem making them your lap dog.
Create Vassal state- ESSENTIAL strategy, you'll get no where w/o doing this, IMHO. Preferably make the ones w/o iron who can't defend against you your vassal. Swordsman rush them until they give you all their tech in negotiations. I don't ever violate peace in 20 turns as I don't want to damage rep. This should get you close to parity w/ other civs. You may have to do this to 2 or even 3 on Deity to get up to speed in tech. In that case, fight one war at a time. Attacking one while you wait the 20 turns on the other. At any rate, continue until you're very close to the leader. All the while your science is at 10% and you should have a load of cash.
Variety of Terrain in borders - keep in mind when expanding to have a broad variety of terrain because you want every opportunity to get those future resources you'll need. See my post on Apolyton
Obtaining Scarce Resources for more on this idea.
Wonders - forget about it during Ancient times, don't even try. Forget the Pyramids and Great Lib. Hopefully one of your vassals will have built them and they're now yours.
Head to Republic - the AI tech advantage is so strong I skip Monarchy altogether, it can be picked up later in some trade. Once I get Republic I should have "vassalized" some opponents and be ready to enter a peaceful period of building my infrastructure.
Expand your Empire - at some point Vassals become useless and it's time for them to go into the history books. You'll have a large part of their territory in your empire and much of if will be corrupt. Build the Faux Palace in their former capital or some where centrally. During the wars you hopefully produced a leader and I will always rush build the FP with him.
Middle Ages
Wartime to Peacetime - Vassals s/b obedient/extinct by now and you can switch to Republic and peace. Concentrate on infrastructure. Should have at least temple/library in every city. Get a colleseum and/or cathedral. Marketplaces are a must. Really any city improvement you can afford should get done now, before your next war.
Wonders - The first one I have a realistic chance at is Bach. I head for Music Theory once in Middle Ages and will start a palace somewhere that I can switch to Bach. If you can't get Sistene (I usually get beat to it), at least go for this one, you'll need it.
Tech Parity - on Emp I can usually get even tech-wise by Middle Ages. I can trade more since I have stuff to offer and do so liberally. I set science up more to 50-60% level. Enough to produce a good profit/turn and still research most stuff in under 10 turns. I usually have a ton of cash from the Despot/10% science days.
Overseas Contact - I have gotten away w/o building any kind of a navy at all until I have destroyers. I make contact because a) they come to my continent or b) I buy the contact from a civ. Then it's trading territory maps and there's no need to explore. Then back to trading w/ new friends. Trade all available lux items, they do no good sitting around in your territory. Get gold/turn.
Democracy - After I switch to this you should be able to get complete parity w/ AI tech-wise.
Middle Ages Units - always upgrade every unit to most modern. AI doesn't always do this so even if your military advisor says you're "weak", chances are you aren't.
Industrial Era
Factories - get Industrialzation and build factories everywhere you can. Don't worry about pollution, production is more important. Now you'll be able to compete for wonders and later SS parts.
Research - by now you should be hitting the 4 turn/tech wall. You should be researching quickly and making a lot of money from trades/vassals. Maybe to the point you can turn science to 100%.
Trading - I start being stingy now. If I have lead, I won't give any tech to those on my heels. I trade backwater civs my real old stuff, that's it. I usually have enough cash by now and don't need their money.
Wonders - Hoover is my main priority here.
Wars - at this point you should have a 30-40 city empire, having taken over your vassal(s). With a tech lead I want peace as I head for space race. I will only start a war over a resource I don't have. I generally will not join any MPP.
Modern Age
Space Ship - by now you should have a firm tech lead and as such the easiest win is space ship. With factories and Hoover, you should have some super producers that will crank out parts in under 10 turns.
Wonders - UN: build it. Just build it if you don't want to lose. Then, of course, Apollo for SS. Most others I have been able to build, too, since I'm in tech lead.
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The strategy hinges on vassals in the early going. Without them, you'll be far behind and won't stand much of a chance. The easiest ones to vassalize are those w/o iron. Make it a priority that someone near you doesn't get it, then crush them. Slowly bleed them of techs in peace negotiations and then eventually take them over. Build FP in their former land and you'll have huge sprawling empire. From there it's more or less standard play in later ages, protect tech lead, play defense w/ most modern units, occasional war for resource, launch ship.
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