Buying a pickup can be as easy as looking at a few videos, hearing a few sound clips, and getting a few recommendations from friends. But with pickup companies like Seymour Duncan making hundreds of different pickups, an educated consumer will be the happiest consumer.
As a guitar teacher, I get asked this question a lot. Since pickups can radically change or expand the tonal options available from an electric guitar, would it be better to just change the pickups or save up for a whole new guitar?
You inherit a rather old guitar, made by a known guitar manufacturer in Kalamazoo, somewhere in the seventies. You play the guitar on every occasion you get: at home, in band practice and on stage. Your band gains some momentum and the venues get bigger and bigger and suddenly you are being struck with a high-pitched, shrieky noise coming from your amp.