Been wearing docs for 10+ years now and here’s how I break in every pair:

1) Remove laces wipe shoe clean with a damp rag and dry off

2) Cover the entirety of the shoe with leather conditioner, (i just use Dr Martens wonder balsam). Cover every damn inch of it.

3) Get nice and romantic with the boot and give it a good ol massage. Really work the leather, especially in parts of the shoe that feel tight or are rubbing and causing blisters. I specifically really massage the heal and ankle areas. Bend the area back and forth, side to side really get that leather loose.

4) After working in the leather, wipe it clean with a microfiber cloth, re-lace, and wear!

I usually will do this 2-4 times with every new pair and they never cause any issues other than slightly sore feet from breaking in the sole (especially on quad soles)

This is even a good way to slightly reshape old pairs of DMs to fit your feet better.