Probably good idea to start with the simple offline regulators: TOPSwitch and the like. Pair with an off-the-shelf transformer, read up on insulation, clearance and creepage, review it here if applicable, test it yourself for performance, range, EMC if possible, etc.
The scope of your design work will be component selection, especially the transformer (inductance, saturation, ratio) to the regulator and application, and ensuring the layout is adequate for safety and EMC purposes.
Then move on to less pre-baked designs: specifying transformer windups (wind them yourself, probably), relating that to EMC response, choosing topology, designing the switch, choosing or designing the controller, etc.
Tim