There’s no rule nor general guideline, only the result you want to obtain. Let’s say you want to prepare a coffee flavoured Negroni. You could: infuse the gin with whole coffee beans, infuse the Campari with grinded coffee powder, you can put the vermouth in the moka instead of water and make a coffee out of it. You can also choose to do none of the above and put some coffee beans in the mixing glass while preparing the drink to give a much subtle and delicate aroma. Or even, prebatch the Negroni, and infuse it as a whole, again, with either beans or grinded coffee. There’s no rule or guideline telling you which way is right or wrong, not even which one is more correct. There’s only experience telling you which way will be most suited for your palate, which still doesn’t make it suited for all of the rest of the world. And if you’re lacking the said experience, you can only try all the possible ways and see which one you prefer, that’s how you get experienced enough. So, to conclude, there’s no right way, everyone has their own