You need good spies, 2-5 assassins, and no enemy FM in the town ( normaly those freaking AI FM´s become administratively inept, but often gain cool ancillaries like "judge", or becomming "drillmasters" with law bonuses when the town riots, depending on the taxe rate ).
The easiest way to let a city revolt is when there are penalties of any kind:

first cultural ( or even freshly conquered, of course )
then distance from capital
and the squalor ( if the town has overpopulation, and the government building isn´t upgraded yet, this is a very good chance to start your plot ).

When a settlement riots, citizens are getting killed, and depending on how large it is, there might be a significant decrease in population so that the public order might stay out of "red face".
Also, AI loves to put the taxes as high as possible, so while you might observe public order of 60% only, this is due to "very high" taxe rate; going to "high" will bring them additionaly +20% public order, to "normal" +45% ( 20 + 25 ), and to "low" +75% ( 30 + 20 + 25 ).
Numerous assasins are needed to destroy multiple buildings in the town at once ( once the AI stops/partially stops repairing damaged buildings, you might need only 2 for the barracks )

- target barracks + auxillery, don´t ever let them stay repaired for even 1 turn, or new units might be recruited
- destroy temples, depending on the size and art of it
- all happieness and law buildings starting with the highest bonus given by them
- once you notice that AI isn´t repairing all buildings at once ( they mostly concentrate on the most vital ones, and the barracks, of course ), you know it´s bit short on money ( you should observe their chash flow in the statistics and hit while they have none; on the other hand, playing on "vh" enables AI to always rapair ( due to 10k mnai cash per turn ) but if you hit the really expensive buildings, it´s still gonna heart ).
You should make sure that the AI has no troops near the town, nor any FM ( assasins and spies suck mostly if FM are present ) which they might bring into the town to boost up the public order.

Also, an enemy spy in the town can destroy all your plans ( enemy spies are almost impossible to kill within a town - "spyguildmaster" trait, no matter how trained he is ).

Well, that´s briefly how i act, but there is no guarantee for your succes - some cities do not revolt, others get "bugged" through you own spy who is increasing the public order instead of decreasing it - in this case try to replace the spy, double them, etc.