Two "old guys" who had been packing for years taught me these techniques for perfection in box packing...a method that best guarantees your items--whatever they are---will arrive at destination in excellent condition:
First, follow the usual tips/guides for "heavily" wrapping individual items that will go into one box. Be sure the box has ample space inside on all dimensions for your wrapped items to fit. Prep the box by setting it upside down and closing all bottom flaps (now on top) in such a way that all flap edges are EVEN with box edges, very straight and neat. Tape the box bottom to retain this very precise shape.
Make neatly squared box dimensions.
Use real packing paper and maybe peanuts, bubble wrap, etc., but not newspaper or magazine pages, paper towels, etc. These latter materials are just not appropriate: will stain china and clothes, will not adequately cushion your items.
If any items for the box will be fragile, you might want to put a cushioning layer at bottom of the box before packing items into it. Then wrap each item individually in whatever packing wrap is most suitable. Fit the various items into the box by leaving some space on all outside edges and between any two items; ample space to now ADD more packing paper and/or those spongy "peanuts."
Now that the box bottom is secure and all items inside are tightly secure, close the box top flaps, same way as bottom: Be SURE that all flap edges are lined up squarely with the box's edges, straight and neat. Secure the flaps with maybe a short piece of tape at centers on top, or at edges. IF YOUR BOX seems as if it's too full and the flaps CANNOT CLOSE perfectly, do either of these: (1) Remove a bit of packing, just enough to enable the box to close with all edges and corners perfectly squared; or (2) Gently push down the inside packing materials, just sufficiently to enable all flap edges to align, and to align with outer box edges.
Tape neatly and amply. No time to be stingy with tape price or tape quality.
One of the "old guys" showed me how he would use the side of his fisted hand to "whack" at a top center side edge of a box side, to push it inward and force it to match up with the flap edges.
Pack and tape squarely.
In these perfect shapes, tape the box securely with good quality tapel
Why do movers and shippers appreciate these tips? Not only because your precious posessions are well protected, but also because all boxes will be very squared, flat on top, securely taped into shape....and thus easy and safe for stacking.
Your boxes wil NOT CRUMPLE and COLLAPSE if you pack in this way. And it takes only a few moments longer than packing sloppily.