Jyväskylä

South-west towards Tampere, Turku (9/E63) or west towards Keuruu (23):

There's a pretty good hh-spot just next to the university's campus called Mattilanniemi. Coming from the center: follow the street called Kauppakatu (the name changes into Korkeakoskentie). There's a bridge for pedestrians over Rantaväylä to the university campus. Don't cross the bridge but go down the small hill to the "shoulder", the side of the road, of Rantaväylä. Walk a bit closer to the traffic lights.

East toward Varkaus, south towards Heinola, Lahti, Helsinki:

This is a bit tricky but not impossible. Coming from the center: Cross the bridge that goes through the trainstation. There's a fair center (Messuhalli) on the other side of the train tracks and the road. Go to the left after the bridge towards the road. Go over a small knee-height fence to the road. Walk on the side of the road a bit more to find a good hh-spot, where the cars have enough space to stop. If this doesn't work out, walk down the road some more until you reach a pedestrian path on your right hand side. Follow it until it goes up in a bridge to cross the highway. Hitchhike before the bridge, because that's where the cars start speeding up.