Expanding on what was said above:
First you need a ship with at least one Grav Survey Sensor.
Prerequisits: Trans Newton Technology --> Jump Point Technology --> Grav Survey Sensor
When you have the ship ready, you should put it into its own taskgroup. To do this, you open the taskgroup window (F12)
If the ship is newly build, it is probably in the Shipyard taskgroup (this is the default TG, new ships are put in).
[attachment=2:34b6jmt7]Taskgroup window 1.JPG[/attachment:34b6jmt7]
Your survey ship should now be in its own TG.
[attachment=1:34b6jmt7]Taskgroup window 3.JPG[/attachment:34b6jmt7]
You can now order the ship (TG) to survey specific survey points manually (you have to activate the checkbox "survey locations"), but you can also let it work automaticaly
[attachment=0:34b6jmt7]Taskgroup window 2.JPG[/attachment:34b6jmt7]
With the "Fuel less than 30%" thing selected, you will get a message about the TG heading for home or, if it can´t get there (no colony within 4 jumps/no jumpship/jumpgate available) a message about it not being able to fullfill a conditional order. Anyway, you will get a message, once the fuel reaches 30%, so there is usually enough to reach someplace to refuel, which is not allways the case with the default, 10% message.