What are the tips to understand the meaning of an Italian saying/idiom if I have never encountered it before?

Italian sayings are quite complicated and there are thousands of them, therefore I would not recommend learning by memory. Instead, it might be very useful to think that, unlike English, Italian sayings heavily rely on the ability to interpret what the meaning is in a more "poetical" way. Let's see an example:"non tutte le ciambelle escono col buco" = "not all donuts end up having a hole" Let's analyse it in a 'practical' way first: when making donuts (without machines that make a perfect circular shape), it is very common that during the cooking process the dough gets so big that the holes close, therefore giving an unwanted result. Now let's think of what it could metaphorically mean: when you make plans in life (making the donut) it is not always certain that the outcome (the donut itself) will be what you expected (having a hole). This idiom can have either a positive or negative acception (you expected something good but the result is catastrophic, or you expected a negative outcome but the outcome turned out to be unexpectedly good)