There is no other possibility to visit Sale than on foot. Streets inside medina are mostly too narrow for any car and even, they are either closed for traffic or there is no place to park a car there.
I followed tourist itinerary marked on a Sale map in my French Michelin Maroc Guide de Tourisme. I started from Bab (Gate) Bou Haja and Bab Khebaz square and walked first main street called Bab Khebaz, too. Well, I surely got lost a few times :-). The walk through the medina to the Muslim Cemetery on the Atlantic coast and back took me with a few stops approx. 3 hours.
I arrived to Sale by own car. I drove along the Moroccan Atlantic coast from Tangier (277 km north of Sale) to Agadir and futher down to Western Sahara. Highway P2 from Larache (216 km) through Kenitra (40 km) to Sale and Rabat was of good quality and not jammed, mostly empty and fast to drive.
I was following quite good although small city map of Michelin Maroc, Guide de Tourisme (my recomendation for folks driving a car, own or hired). And, as always in Morocco, when my highway reached city walls I drove along them looking for a safe place to park a car. In Sale it is quite easy: driving southwards keep along city walls = turn right on large roundabout and you are on the street on my picture. I turned U just before the street crossed city walls and easily parked a car on a street. There were no "parking guards" offering care about my car and ordering money in Sale.
I saw large bus station outside eastern city wall (along main highway P2: Tangier - Rabat) and I got to know that there were city buses from and to Rabat there. Alternative (more expensive but still cheap) is to take a taxi or (less expensive and less comfortable) shared taxi from Rabat to Sale.