The first thing I want to know is why your concrete wore out or cracked. A new surface won't fix a slab that's sinking or breaking up, any more than fresh paint fixes a bent tractor frame. If the slab is solid, we sit down and go over finish choices with you. If it isn't, I'll tell you so, and we'll talk about what it needs first.
On a sound slab, our crew does the prep before anything else, because most of the floor failures I've seen started underneath the surface. We clean the concrete down, take off loose material and old coatings, and repair cracks and chipped spots so the new surface bonds to good concrete. Only then does the overlay go down.
Some floors need a different job. If an inside floor runs out of level and has to come back flat, self-leveling concrete and overlays is usually the better fit. The concrete around a pool sits wet and takes bare feet all summer, so we handle that as its own job under pool deck coatings and resurfacing.