If you mean anything like prospecting it's really not something a random guy just goes into. Most likely you need a masters degree and then you just get hired by a big company and they train you and supply equipment. It is possible, more for minerals than oil, to go it your own, but it does require rather extensive knowledge of geology.
Like the most basic bitch type I can think of is gold, then you want to find quartz veins in rock because, like gold, it's hydrothermally deposited so they're often coincident, but just because there is quartz does not mean there's gold. Or like going downstream from teh metamorphic or igneous rocks to sedimentary areas, because it gets eroded out of the rocks and obviously travels downstream and you get into panning. But you have to look into the legal shit and various claims and whatnot, and of course all the obvious areas are all take.
There are all sorts of geophysical methods for attempting to detect valuable resources, but again you'll need rather extensive knowledge to know what they are and how to even use them and what the data you generate even means.
tl;dr go to school I guess. Or really dig in to the literature (economic geology is what you're going to want to start with assuming you know the basics of geology already (particularly petrology & mineralogy)).