Most blisters from new shoes come from friction in two spots: the back of the heel and the outside of the little toe. A stiff new upper has not yet learned the shape of your foot, so it moves against the skin instead of with it. Breaking in is just the process of that material softening and settling — you can make it faster and kinder, but you cannot skip it.
Start indoors, start short
Wear the new pair around the house for an hour or two a day for the first few days, in the socks you will actually wear with them. Warm feet soften the upper from the inside, and you can take the shoes off the moment a hot spot appears rather than being stuck at the office with it.
This is also your last chance to return them. If a shoe hurts across the ball of the foot or pinches the toes after a week indoors, it is the wrong size or the wrong shape, and no amount of breaking in will fix that.
Socks do half the work
Friction happens between the sock and the skin as much as between the sock and the shoe. Merino or a merino blend moves moisture away and slides less than cotton, which is why hikers swear by it. For a low-cut shoe worn without visible socks, the only no-shows worth owning have a silicone grip at the heel; the ones without it slip down and bunch under the arch, which creates exactly the friction you were trying to avoid.
Fix the heel before it fixes you
If the heel slips — the shoe lifts as you walk — the back of the shoe rubs up and down against the skin with every step. Two things help: lacing through the top eyelets in a runner's loop to lock the heel down, and a slightly thicker insole to lift the foot and fill the space. If the heel is still slipping after both, the shoe is too long.
What makes it worse
Wetting the shoes to stretch them. It works on some leathers and ruins most other things — glues, foam, finishes — and the shoe dries stiffer than it started. Hair dryers, same reason.
Wearing them for a full day on day one. A long walk in an unbroken shoe is how a hot spot becomes a blister that keeps you out of the pair for a week.
When it clicks
Somewhere between the fifth and the fifteenth wear, the shoe stops being a thing you notice. That is the point where a shoe tree becomes worth it: the shape it has just learned is the one you want it to keep.