We found getting here really easy - catch the train from Tunis to Jendouba, out of the station and a quick trip to the bus station and a bus was waiting to take us to El Kef.
Easy also to get to Terbersouk (for Dougga) - lots of daily busses
Getting to Sousse was a liittle more complicated. We had been told that a bus was due to leave at noon, taking about 4 to 5 hours to make the trip. Pretty convenient we thought. Of course, when we got to the bus station, after a leisurely morning in El Kef, no such bus was in evidence. After about an hour of waiting in queues, holding spaces preparatory to rushing onto buses, we found a bus would leave at 2pm, getting to Sousse at about 6pm.
In retrospect, it might have been less stressful to take the bus back to Tunis and catch one of the many trains down to Sousse.
The louage and bus stations lie close to each other down in the new town. Just head downhill on one of the roads from Place de l"independence, and you'll find it. Coming from the louage station, head uphill until you reach a junction, then turn right and follow the road to get to Place de l"Independence, which isn't really a square at all, but more of a bend in the road with a view of the old town and kasbah above.
Buses head to all destinations in Tunisia, as do louages, although louages are probably a better bet as there will be one filling up at the time when you want to travel. Jendouba is just over an hour away, not much of a destination in itself, but the best place to arrange onward transport to Bulla Regia. You also change here for Beja, Bizerte and other destinations in the north. For the Roman site of Dougga, louages heading to Tunis pass through Nouvelle Dougga, 3km from the site, and other louages can take you to Teboursouk, also not far away. I heard louage drivers calling out for Gafsa, a town with Roman pools and an oasis on the way to Tozeur. I took a louage to Sfax, 4 hours away, which cost me 12TD.
There is a very smoky cafe next to the louage station, which is very handy as for some destinations you may have to wait a while for the louage to fill up. There are also stalls selling fried sausage sandwiches which smell great and don't taste too bad either.