Valence is a city in France. One highway is linking Marseille to Lyon, and another highway is going towards Grenoble and Italy.
North/South towards Lyon, Paris, Marseille
To get on the A7, you have two possibilities : Valence Nord (North) or Valence Sud (South). I much prefer the on-ramp at Valence Nord, because there's more space for cars to stop. I never waited more than 30 minutes at this spot. I use it to either go North or South, but most cars are going North. I have to sometimes decline a few cars going North if I want to go South, but I always end up finding a car rather quickly. Going South : The first service area is soon after Valence South, so if a car is going past Valence accept the ride, and get dropped at this service area to search for another car. Going North : Most cars are going to Lyon, and if you don't you'll have to get down at the toll near Vienne (there's a parking area with a few cars) or before in a bigger gas station.
East towards Grenoble, Italy
There's a massive roundabout near the shopping area "Les Couleures". There's a bus stop not far from there. You can stand at the entrance of the national road N532 towards Grenoble. It becomes a highway after 30-40 kilometers, but there are a few service areas in between. There's enough space for cars to stop.
Accommodation and Sleep
You can probably get away with camping for a night near the Rhone river.