What is a Rush?

To attack an enemy sometime before Imperial Age when
they are not prepared/not expecting/  an attack and to
kill as many of his villagers as possible.

Most good players will do a rush of some sort before
Imperial age.  There are many ways to perform a rush,
with different units,building and civilizations.
Research The Loom
Get the upgrades needed to make your attacking force stronger.
Get at least one tower or TC to heal wounded units or to retreat
to until your next wave is ready and to act as a forward base to
around.
A Monk or 2 healing your wounded units can be deciding factor in
tough fights.
Before doing any rush Scout!

Harassment/Deceptive Rush           Probe Rush
Slow Them Down Rush                 All Out Rush
Tower Rush                                  Town Center Rush

Harassment/Deceptive Rush- sending a few units at a
time to throw your opponent of his game plan or to slow
him down, while you are working on advancing in age.
Your not really looking to kill villagers(although
kill as many as you can get), you want your enemy to
ring his town bell(slow down food production), start
building towers and walls(whatever vils are assigned to
these task will mean less resources coming in),  force your
enemy into building a large army with upgrades to fend off
your attack(puts a real damper advancing to the next
age).  To make your opponent build army composed of
the units that you want him to build.  If you rush in Feudal
with scouts your enemy will counter with Pikes most of
time.  He will mostly likely build enough to kill off your
Scouts, then continue building Pikes in anticipation of
you next wave.  Now the stage is set for a Castle Kill.
Your enemy will probably get to castle when you have
already  built your Castle army composed of infantry,
siege, archers.  If you attack with Men at Arms in feudal
and your enemy counters with MAA and Archers, just
attack with Knights and siege.

Probe Rush- Starts out the same way as a Harassment
/Deceptive Rush.  Depending on what your your enemy
does sets the course of you next action.  For instance,
if your enemy easily defeats your probe units.  Is well
defended.   You realize that it will cost you more in
food and gold  than he is losing in villagers.  Then  you
may choose to attack at a later time.  On the other hand
if your target puts up little resistance, you may wish to
finish him off now, realizing that there is less chance
of allied help coming to his aid this early in the game.  Or
you can  just to choose to him down.

Slow Them Down Rush-  This rush is to hurt your enemy
as much as possible, without leaving yourself to
vulnerable to other enemy civilization attacks on your
Town.  Generally 10 to 20 units  composed of 1 or 2
types.  Halting production of new units or using new units
for a  home defense.  You may choose this option even
if you realize you can defeat your opponent now for a 
few reasons.  Your allies need your help either in
attacking or defending .  You suspect an attack on your
base.  You do not wish to be to far behind your enemies
in advancing to the next age.

All Out Rush-  Putting most of your effort into defeating your
enemy here and now.  Leaving little protection  in your home
base.  Your economy should is geared for building the units
that you are using for the rush. 

Tower Rush-  Building towers in an enemy base cutting
him off from his resources. 

Town Center Rush-  This  involves  rushing to Castle before
your enemy. switching  your economy to generate allot of
wood.  Building Town Centers in the enemy camp forcing
him away from his resources.  A couple of  TC rush games
are available in the Recorded games section.  This rush is most
commonly done by the players using the Teuton civilization.
The Teutons are perfect for this because of there +2 attack
+ 5 range for their TC's, although any civ can use this rush
effectively.