As for dealing with corruption; it is sometimes more favourable to spend six turns "building" a town/city guard (or even better, improved roads or baths) than an equivalent or greater length of time building something that might only boost trade income by a handful of mnai per turn.
Corruption is directly affected by "LAW". The more buidings improving "LAW" will reduce corruption.

I just have one doubt regarding city building, one that i have never managed to discover after countless tests. What is "Unrest"? What causes "Unrest"?

I have heard that having a "blue" face or anything below 75% will gradually increase unrest and having more then that will reduce it slowly, but i havent had any sucess and noticed no difference after having a city more then 10 years with about 150% public order.

Seriously, Unrest is a killer in most of my cities - in some cities it even reaches about 50%!