Pickups, potentiometers, capacitors, resistors, switches, jacks, and wiring can all wear out or at least become suspect in the sound of an electric guitar. Over the years, volume and tone pots can become scratchy due to
lack of use or from exposure to moisture causing oxidation and scratchy sounds when turned.
Swapping out stock pickups for new after-market pickups is a common way to greatly improve the sound quality of the guitar. Seymour Duncans and Dimarzio are common replacement brands, but there are many others that can
be selected. Just tell me what sound you're looking for and a pickup or pickup set can be selected and installed.
Heavy lifting is an option too - neck and fret re-work, that is, replacing frets, the nut and tuning machines. Better tuning machines and a new nut will help hoding the tune of the guitar.