The answer for pirates is similar to the answer for other commerce raiders (such as, for example, privateers or private men-of war, or regular naval vessels): there were basic and known shipping routes or landfalls that ships could reliably be assumed to sail past, especially in the days before the 'invention of the longitude," that raiders could lurk at or near with a chance of intercepting ships. The reason for there being well-traveled shipping routes is threefold:

• first, ships that carry commerce need to touch at ports or at least settlements, inlets or streams, to trade their goods and to replenish their food/water before sailing on. So lurking outside or near a port gives you a high chance of seeing ships.

• second, before there were reliable methods of discovering one's longitude (that is, one's east-west position on the globe) the most common way to approach land after being out of sight was to find a known line of latitude and "run down" that line until making landfall. That's one of the reasons we can talk about known landfalls in the day of sail; ships would have to find a spot of land to orient themselves to, and keeping a ship on station near there heightened chances of intercepting commerce.

• third, the geography of many places and the prevailing wind means that there are only so many places where ships can actually pass through or by points of land. The obvious strategic chokehold that comes to mind is the Straits of Gibraltar, which were of massive strategic importance to Britain after Gibraltar was taken in 1704 (and the Brits are there yet), but in the Caribbean the Windward Passage between Cuba and Haiti and the Leeward Passage in what's now the US Virgin Islands were shipping routes that are narrow and easy to cover with a small squadron.

To get so some of your specific questions:

Would pirates have had intel on where to intercept shipments or did they simply sail around looting random ships?

Well, a major target of pirates during the period of Spanish rule in the Caribbean was the wealth that Spain extracted from the New World to send back home, specifically the annual flota or treasure fleet. I wrote more about this here; because the flota followed a known route, its capture was mooted by pirates and privateers as well as English-sponsored expeditions; but in the event only one flota was ever actually captured over a period of 300 years, by the Dutch East India company in 1628.

Were these pirates usually taking gold, silver, etc.? Would they ever loot, say, shipments of tea or other inventory?

Pirates were very much mostly taking shipments of small goods, and very rarely actual shipments of gold and silver. The raiders who were most successful at intercepting actual treasure did so generally by looting cities, and people such as say Henry Morgan or Francis Drake who did so were operating in more of an official capacity than most pirates, though the Spanish authorities thought of them as pirates. (I wrote more about the 16th c. in the Caribbean here previously.)

But the point that gets lost in the romanticization of pirates is that for the most part, they were just common criminals -- they routinely destroyed people's livelihoods; tortured people for fun; raped and killed people; burned towns and churches; and fought viciously amongst themselves. They were for the most part criminal bands of desperate thugs and an irritant to society.