It is highly recommended that you use the Patcher to install the mod, however if for some reason the Patcher doesn't work you or you can't get it pass your firewall you can download the full mod and install it manually using the steps bellow. You don't need to run the Patcher if you manually install, even though it is included in the zip, you only need to run the mod's exe.
The Improvement Mod can be downloaded fully from here to install over a clean installation of AoE3 Complete Collection (preferably Steam version) manually. The Patcher can be used to keep the mod up-to-date, however the Patcher is NOT required to be ran in order to play the mod. To play the mod you only need to run "age3m.exe".
AoE3 Complete Collection is recommended for the Improvement Mod, which is also the Steam version. You could install the mod over other versions as well but you would need to have the game plus both expansions installed (TWC and TAD) and ALL official updates.
To install the mod just download the zip, open the game's main folder where all the exes are (for the Steam version ALWAYS INSIDE THE BIN FOLDER), and unzip the contents so that the mod's exe files are along side the game's exe files. Common AoE3 install paths are:
/Steam/steamapps/common/Age of Empires 3/bin/
/Program Files/Microsoft Games/Age Of Empires III/
(additionally you should put "age3m.exe" in Windows XP SP3 compatibility mode so settings are saved properly)
If you have any problems be sure to ask for help here or on the mod's blog.