How to win proxy wars than?

people told me that winning in proxy wars, especially in italy, spain and bulgaria is important as germany.

But how do you win specifically? for example when I need to support socialist spain I usually push carlist by going through north costal cities. this is my only example of having plan in proxy wars.

I think I losing proxy wars because I don't have plans, I usually play defensively and passively because of my lack of plan.

Is there good genral plans like this to help monarchist spain, two Siciles and bulgaria?