Many have asked, so here are all the ones I've discovered so far, including
one or two I read here:

[IMPORTANT: first thing to do is set the "end of turn" option on, as
many of the following will be difficult to do without it]

1: Settlers - settlers can build roads, irrigate, build railroads, or
control pollution or mine all in one turn. After all your pieces have
been moved (or in the case of roads/railroads where you wish to use
said road/rr, before) click onto the settlers again, and hit r/i/p again.
Repeat as many times as necessary for said operation on square (the
computer will not let the settlers do anything else once one improvement
has been completed)

2: Ships - ships have interesting effects on piece movements, and can
be used very advantageously during the game. Build enough ships to space
them their movement allocation apart between continents, including being
docked in cities. (This is important!!!) When you want to move a piece
from Spot A to spot B on another continent and you have this convoy
setup, you can do the following: Move piece into first city with docked
ship, and have piece go into sentry mode (do this for all pieces to
be moved) and then activate ship (docked ship can be in sentry mode,
it will not affect movement points) move ship out and then onto next
ship in line, then activate that ship. (It will automatically take over
all the pieces as passengers it can hold) move it onto the next and
so on, until you dock into the destination city. Now, click into the
destination city, and activate *all* the pieces you just delivered (they'll
appear to be in sentry mode) and exit city. Voila, you now have *full*
movement points restored to all the pieces you've just delivered, effectively
getting two complete sets of movement points in one turn.

(Note: I figured this last part out when I was already using transports,
and have not yet gone back to discover whether trimerenes and sails
do the same, although I expect they work similarly)

This also works best with railroads, as then you can have a small military,
yet deploy them world-wide in one turn. It keeps the populace much happier
on the whole when you're running a democracy.

I've just finished a game at emporer level (Yes, Suleyman the Wise is
after Emporer Augustus at 140%:) wherein I had dominated the world by
2700 BC. (I'm going back to that point to see what my rating would have
been had I finished conquering everyone at that point, and whether it
would have been worth doing it instead of growing to 30+ million population
and launching a space ship, and building all the wonders (or stealing
them).

Strategies: Start and obtain bronze working, the wheel, alphabet, and
writing and literacy with science set as high as it takes to reduce
the advance to a minimum number of turns. (See trade advisor to set
the tax rates to obtain as much money as possible while gaining science
at the highest possible rate.) You want Literacy so that you can build
the Great Library Wonder, and gain any new advances made by others.
Writing allows you diplomats so that you can steal anyything you don't
find yourself first or gain through the Great Library, as well as force
meetings between yourself and rivals when peace is desirable (such as
you've just taken over a city, you have no defensivce units, and the
enemy is coming upon you)

Find your neighbors on the continent as quickly as possible
(I build to or three militias and send them searching, not bothering
to defend my city.  If I loose, I prefer to do it in the first ten minutes,
not after devoting several days to a game) Build a phalanx as soon as
you obtain bronze working. Build a granary to allow your city to grow
as fast as possible. Once you reach a size of 4, you'll need a temple,
so build settlers to keep your city(ies) to a size of three until you
obtain ceremony. You'll want to get out of despotism as soon as you
hit about 5 in size, so you'll need code of laws and monarchy now. At
this point, maintenance will become a problem so you need currency and
trade (mathematics is in there also). By now, you should have taken
over *all* your neighbors (it's easiest to do this early, when no one
has built barracks and is fielding veteran phalanxes to guard them,
and even if they are, until they have city walls, chariots romp right
over them) Try to incorporate as many of these cities into your empire
as possible. Now you'll need navigation quickly, but build trimerenes
to investigate the surroundings quickly, and possibly make early contact.

    Contact: make sure that you leave some of the cities of other civs
alive at this point, as you need them for trade. Generally, I leave
the capitals, and take over all the other cities, then remove the weakest
capitals and leave the largest three for trade purposes. (I'm of the
thought that your highest score will come from sending the spaceship
off).

This should be enough to make even the Emporer level fairly easy, although
it by no means is a full strategy. Other things are the following:

Pollution, large cities produce pollution with the discovery of the
automobile (cities size of ~20) with *no* production. Need mass transit
to offset this.
Recycling and mass transit combined allow for no pollution to be produced
with up to 62 resources.

Happiness - large cities will generally not have all happy people, so
to increase your score, build settlers and found cities of size 3 or
less with high luxuries at end of game (ie year before spaceship lands)
Also disband all bombers and nukes in a democracy (perhaps all military?)
before this occurs. Otherwise, a city of size 4 requires a temple, of
size 5 or 6 a marketplace for all citizens to be content.

Large cities (size 20 or more) are excellent sources of revenue for
extra-continent trade after you've established your three trade routes
for each city. Have high production cities (not necesarrily the largest
population) produce caravans, and (with rr) send them to the large city,
then across to the other continent to the *largest and most powerful*
of the remaining capitals. (I made over 110 coins per caravan sent,
built ~8 caravans a turn on this one continent) doing this, and my costs
were only 650 coins per turn. (My tax revenue was about 3000 coins per
turn) This allows you to buy all improvement for new cities befoore
the population even reaches 2, and gives it full trade routes also.
This is the quickest way to grow cities. (less than 70 years, 1840-1910
to go from size 1 to size 10-15) it also allows all production to center
in on a few cities, with the corresponding costs associated with those
improvements, while allowing the rest to concentrate on growing and
trade only.