How Do I Prepare My Kitchen for New Countertops

A remade template visit costs a half day of the fabricator's time, and a cabinet that is out of level by a quarter inch can force exactly that. Prep before a stone top goes in is mostly small jobs that cost little when done early and a lot when done after the slab is cut. For a custom kitchen in Riverside, CA, the order matters, as the notes at custom countertops riverside spam archive describe.
Cabinets first

Cabinets must be level, square and firmly fastened before templating. The template records the cabinet tops exactly as they are, so a dip or a gap stays in the measurement. Stone will not hide it and it will not level out a bad run. Shim and fasten the boxes, check the tops with a long straightedge, and fix the low spots before anyone marks a template. Granite and quartz are both rigid and will rock on an uneven base.
Sink, faucet and cooktop

Choose the sink, faucet and cooktop before templating, and ideally have them on site so the cutouts follow the manufacturer cutout dimensions. An undermount sink is attached to the underside of the stone, so the actual sink must be available before or on install day. A sink picked after the slab is cut means a guess at the opening, and a guess is how a cutout gets ruined.
Dishwasher, overhang and supports
Stone cannot accept screws from above, so a dishwasher is usually secured with side mount brackets into the cabinet sides instead of the countertop. Seating needs its own check. An overhang beyond what the stone can carry on its own typically needs steel brackets or corbels, and those get planned before templating, not after. Marble and soft stones are less forgiving at a long overhang, so the edge profile and the support are decided together. Seam placement is also settled at this stage, since it depends on slab size and where the supports land.
Demolition and the wall behind
Removing old tile or laminate tops can damage drywall or the backsplash area behind them. Plan for patching before a new backsplash goes on. In older Riverside homes near Mount Rubidoux, walls are rarely straight, and a torn-up wall behind the range shows up fast once a flat stone edge sits against it.
Plumbing and access
Plumbing is disconnected before removal and reconnected after install, so book the plumber around the install schedule. Leave the water off only as long as needed, and have the plumber return the same day or the next. Do not leave a kitchen without a working sink for a week because two trades were booked independently.
Clear the path
Clear the countertops, the cabinet tops and a path from the entry to the kitchen. Installers carry slabs on edge and need room to turn, so move planters, rugs and furniture out of the way. In the Inland Empire, summer heat makes a long carry worse, so open the doors and keep the route short and dry.