Some Cadsoft Eagle tips and tricks that don’t appear elsewhere.
Add text with >DRAWING_NAME on the PCB to automatically store the text name (which contains the version number if you’re saving files that way) on the PCB to know exactly what file the PCB is from.
Use Falstad Circuit Simulator for quick mockups/sanity checks/value tuning and save to schematic as text for later reference/debugging/blame assignment.
Eagle exports very nice .DXF — much better than Inkscape, Illustrator, or CorelDraw. Eagle can be used to quickly draft small parts for laser cutting when AutoCAD or Draftsight is overkill.