I have Slic3r put it into the G-code for me automatically whenever I slice anything.

Printer Settings tab
Custom G-code

M190 S[first_layer_bed_temperature] ; set bed temperature, wait for it to reach target before proceeding
M117 Homing...
G28
M104 S[first_layer_temperature] ; set hotend temperature. Use M109 to set and wait
M117 Auto Bed Leveling...
G29 P4 ; auto level
G1 X99 Y99 Z1 F1500; reposition extruder
M109 S[first_layer_temperature] ; in case the hotend didn't heat up fully during ABL
M117 Printing...