Here is the "preamble"
M106 S0
M140 S60
M104 S204 T0
G28 ;move to endstops
G21 ; set units to millimeters
G90 ; use absolute coordinates
M82 ; use absolute distances for extrusion
G92 E0 ; reset extrusion distance
G1 E-4.00000 F900.00000 ; retract
G92 E0 ; reset extrusion distance
M190 S60
M109 S204 T0
G92 E0 ;zero the extruded length
G1 F200 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again
G1 F12000