First, you should get your BPT up to 20 by building construction sites. After that, you should choose a government that helps your strategy, which you have chosen to be casher.
I'd recommend Republic (For the 20% PCI and explore bonus), but you can also choose Theocracy (for the faster construction, cheaper military, and 50% population bonus).
Once your BPT is 20, you should alternate building more construction sites and equal amounts of enterprise & residential zones. Don't worry about any other types of buildings, the enterprise zones and residential will be much more beneficial. You should try to get your BPT up to around 50 - 60, depending on how much land you plan to get.
Once you've reached 50 - 60 BPT, you can continue to explore and evenly build enterprise and residential zones, but try to buy residential and business tech when you can, as this will increase your income. (Maximum is 180% unless you choose Theocracy, in which case it is 152%; Try to get close to the maximum)
Keep in mind that you will have negative food income, be sure to buy food as needed. Resist building farms, it will be much more efficient to purchase it from the public market.
Be sure to look into batch exploring & stocking/destocking
For a more detailed guide, visit the wiki:
http://wiki.earthempires.com/index.php/Casher