This is a simple guide that aims to help you manage your empire, so lets go for the start *this guide is still under construction!*
Research
My first opening move is to get as fast as I can ballistas. Simply because they can give your armies a very large advantage in the field, I usually equip 4 units of ballista in my army and use mainly levy quality troops, and they will win even during the middle part of the campaign. The fights will indeed become tougher as time progresses, but you have a very cheap army and doesn't weight heavily on your poor starting economy.
After that I go for the lvl 3 library research, its usually 2 or 3 researches in the philosophy tree, and that will give you a very healthy boost in terms of research speed.
We researched the libraries and thus I usually focus on unlocking the lvl 2 factional barracks (in the romans case lvl 3 barracks), after that its pretty much economical research, get lvl 3 farms they are essential to you and depending on your faction, for example rome, you can get a lot of income while you get food as well with those ranches.
And here is the crux's, I put in every province capital a library of at least lvl 3, this gives you a very large and unfair tech advantage against the AI. Depending on the faction I have finished all the researches around 90bc, yes I have gone through the whole tech tree.
So I can't stress enough that you should focus on research and ways to speed that up.