There are two main trouble spots in DC-DC converter design - protection and noise.
A switching power supply is a dead short across its input once the inductor has saturated. The switch, usually a power MOSFET, needs to turn off on every cycle before that happens. Otherwise, something will fail and probably burn out. Also, the failure mode of power MOSFETS is usually "on". So protection circuitry is needed. Fuses, current limiters, etc. This is why UL approval for switchers connected to the power line is important.
Switchers work by generating big inductive spikes. Those spikes are supposed to be directed into capacitors and smoothed out into DC. Without suitable filtering, spikes will be pushed into the power source, the load, and the RF spectrum. A few ferrite beads, Zener diodes, and small capacitors in the right spots will fix this. LTSpice simulation is useful in picking the component values. You're not done until both the current and voltage curves are flat.