Given the practical value that would come with knowing the future, it's not surprising that many forms of divination have developed across many cultures. While some forms of divination strove for a somewhat objective method of interpretation by allowing only yes/no answers, many forms were quite ambiguous. A believer might attribute this to the difficulty associated with peering into the future, the cynic might note that such ambiguity allowed ancient diviners to claim a higher success rate.
Among the ancient Etruscans and later Romans (although likely borrowed from other earlier cultures), one common form of divination involved examining the entrails of animals particularly slaughtered as part of ritual sacrifice. This type of divination, like many types of ancient divination, required a specialist: a haruspex. in general, haruspicy was supposed to be conducted in conjunction with different techniques provided by other divination specialists, similar how many modern studies often involve two different scientists independently examining the data. The haruspexes themselves also tended to have some knowledge of interpretation of other omens, such as the meaning of lighting strikes (obviously, that type of divination was a bit less human-directed and controllable).
The haruspex was supposed to fast for a decent period, anywhere from a half-day to three days before the procedure. They were supposed to pray and have a proper mindset to beseech the gods for aid. This was often supposed to come as part of a meditation period where the haruspex concentrated on the question being answered.
An animal, typically something like a sheep or a chicken though occasionally something more grandiose like a bull, would be ritually slaughtered and its organs extracted. Different organs may be used for inspection, but the liver and heart were common. The haurspex was supposed to example patterns, folding, bumps, and other markings in particular areas that were supposed to correspond, potentially, to different particular interpretations based on their links to particular deities. So, in theory, this type of divination was at least attempting to be more precise but given the tremendous amount of liberty about determining what was worthy of note in a particular region, a lot of the ambiguity was retained.
Archaeologists have even found an Etruscan liver model that was either a "practice" liver or a handy reference tool:
The Piacenza Liver: An Etruscan haruspicy practice liver
After conducting the divination procedure, the slaughtered animals would typically be consumed in a feast. Waste not, want not.
Although many forms of divination throughout history have been associated with major events, there is one particularly important ancient Roman event wnere haruspicy was involved. The diviner who allegedly warned Julius Caesar to "beware the Ides of March" was a haruspex. In that case, I suppose one could chalk that up as a "success" for haruspicy.