Start with the right box, not just any box
Dish barrels with cell dividers are built for glassware and stemware, and picture cartons are sized for framed art and mirrors. A regular moving box asked to do either job usually ends up either too loose or crushed under its own stack weight.
In Santa Clarita's dry heat, cheap boxes that have sat in a garage for weeks can already be weaker than they look, so it is worth starting with fresh material for anything genuinely breakable.
Wrap for the trip, not just the shelf
Wrap each fragile item individually in packing paper before it goes into the box, and fill every gap so nothing can shift once the box is sealed and stacked. A plate that rattles inside its own box is a plate that is going to crack somewhere on the drive.
For a long-distance trip out of the valley, add an extra layer of padding around anything especially delicate. Highway miles and a hot trailer are harder on fragile items than a short local hop across town.
Electronics need their own approach
Photograph the back of any television or computer setup before disconnecting cables, then bag and label each cable so reassembly at the new place is fast rather than guesswork. Original boxes, if you kept them, are still the best fit for screens.
Keep electronics out of a hot trailer as much as possible. If you are driving separately, carrying laptops and smaller devices in your own car is often the safest option on a summer move.
Loading order matters as much as the packing
Fragile boxes should go on top of the stack in the truck, never underneath heavier furniture, and they should be loaded last so they come off first at the other end. Mark every fragile box clearly on more than one side, since boxes get turned and stacked during the move.
If you are hiring packers for just the fragile rooms, tell them which pieces have sentimental or replacement value that matters most, so extra care goes exactly where you want it.