Follow the road that goes out of the town towards the La Vina neighborhood (Ctra de Granada), until you reach a roundabout with fountains. For Granada, you can hitchhike on the road just before the entry to the motorway, there is a reasonably good spot at the road crossing. Be careful though as the traffic might be high
Go to the highway junction east from the city. You can hitchhike either on highway entrance or already on the road leading there. Take rather the east exit and not the one north from the centre as on the north one is less traffic.