Pre Fix

G90 ;absolute positioning -   .
M82 ;set extruder to absolute mode -    .
M107 ;start with the fan off -    .
G28 X0 Y0 ;move X/Y to min endstops -  XY.
G28 Z0 ;move Z to min endstops -  Z.
G1 X0 Y100 Z15 F3000; go start positions
G1 X10 Y100 Z0.5; go near bed level
G1 E9 F300; extruse a bubble
G4 S5 ; wait 5 sec
G1 Z5
G4 S3 ; wait 3 sec
G1 F3000
G1 X20 Y100 Z0.25
G1 X25 Y100

Post fix
M104 S0 ;extruder heater off -   .
M140 S0 ;heated bed heater off (if you have it) -   .
M107 ;fan off -    .
G91 ;relative positioning -      XYZE.
G1 E-1 F300 ;retract the filament a bit before lifting the nozzle, to release some of the pressure -   .
G1 Z+4 E-2 X-20 Y-20 F3000 ;move Z up a bit and retract filament even more -     .
G28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way -  XY.
M84 ;steppers off -  .
G90 ;absolute positioning -    .
