I started about 20 years ago by looking at application notes from Unitrode, SGS (now STI), Motorola, Philips etc. after studying the basic topologies and equations that governs them. One point of good advice I can give you: Don't neglect the magnetics construction or you will be disappointed! Take great care if you have to construct any ferrite choke or transformer, and pay attention to winding layout, layers stacking, insulation etc. At higher frequencies > 100kHz leakage inductance becomes a real problem and will come back to bite you in the form of voltage spikes and blown devices. Start with low power designs and work your way up to the big stuff. This way you will build up confidence and learn from your mistakes (may be very costly at high powers) blowing up a 150A, 500V IGBT device on a 37kW switcher (happened to me years ago) does not make the boss very happy! You will learn how to take precautions at high power (de-saturation detection, current slope trips..) as you get more experience. Also from Murphy's "The transistor will blow to protect the fuse" is very true. As one of my friends used to say: "Remember the fuse is only there to prevent the whole damn building from burning down"