The Strategy Safe Scan is done by sending two spy probes, the first one you send to scout for resources or enemy fleets, the second one you send just after you send your fleet but be sure to slow your spy probe's speed down so it's just a tiny bit faster than your fleet,

this way your spy probe will arrive first to check for any hidden or recently built fleets that your enemy might of moved, and if it finds something you can recall your fleet preventing an ambush.