Have the proper tools

This doesn't have to cost a fortune.

Your skill level Tools to own Tools to get access to
  • Miscellaneous hand tools - phillips and flat screwdrivers, pliers, files, hammer (for making bad components into dust...)
  • Simple soldering iron, 30W or less - too hot is bad news
  • needle nose pliers
  • small diagonal cutters
  • rosin core solder, fine sandpaper, steel wool
  • braid-type solder remover
  • cheap Digital Multi Meter (DMM) with ohms, volts and current
  • Audio Probe made from an enclosed phone jack, a capacitor, and a guitar cord.
Oscilloscope or PC based o'scope if you can. You may not need it for many things.
Learner All that and
  • A better DMM that also measures transistor gain, maybe measures capacitance.
  • A test oscillator for driving signals
  • Solder sucker
Oscilloscope or PC based o'scope (like through a sound card)
Advanced All that and an oscilloscope if you can at all afford it. Oscilloscope for certain
Wizard All that and an oscilloscope for sure. Maybe a distortion analyzer.