You use G94 at the head of your G-code and it's all.
Use G1 X## Y## F400 to change your speed.
For example:
G94
G0 X0 Y0 Z0 - it's fase movement
G1 X300 Z-4 F600 - move to this point with speed 600 units/minute
G1 X200 Y200 Z-10 F200 - change speed
M2
Read
G-code quick reference
for more details