Not currently in the middle of one, but my last one went pretty well. I owed my success to a simple strategy:
1. Build Ninjas. 4+ of them. Build 1 or 2 Monks.
2. Send Ninjas so sabotage every rice farm they can find. If no Rice farms are nearby, sabotage Markets, Temples and Sake Dens.
3. Send Monks to demoralize armies and maybe convert some agents until they get the +4 to incite unrest skill.
4. By this point the clans whose farms you were burning are bankrupt from rebuilding them all the time and their provinces are either rebelling or at low public order due to starvation.
5. March your Monks into the low order provinces and start inciting unrest (higher chance to work if public order is low).
6. Wait for the targeted clan to be destroyed or crippled by massive rebellions in all their provinces.
7. Move in to sweep up rebel-controlled provinces and minor clans that resulted from 6.
Congratulations, you just wiped out some dudes without ever declaring war on them. All you did was fight rebels and malcontents. A clan of your honor would never declare war on another major clan, now would you...
