Most new and reman clutch discs these days are either stamped FLYWHEEL SIDE or have a sticker that says it. Otherwise the flatter of the 2 sides should go against the flywheel and the protruding hub into the pressure plate.
A quick double check on most engines is to place the disc up against the flywheel and try to turn it. If it won't turn smoothly or you feel anything catching on it then it is backwards.
Points of interference are the dampening springs hanging up on the flywheel bolts or the splined hub is up against the crankshaft / pilot bushing. Depending on the counterbore diameter of the flywheel the steel hub ass'y of the clutch may hit the face and the disc itself will not even be able to contact the flywheel face.
