In basic training we broke them in by smothering them in boot polish and setting fire to them, then we polished all the pimples off with a red hot spoon handle and finally rubbed them up to a mirror finish with lots of polish, plenty of spit and the infamous yellow duster. Our drill instructors kindly helped us with wearing them in by marching us around a lot - to save us walking.
After moving off to the real RAF, in No 1 Group, Bomber Command, we were issued with 'previously owned' working boots so wearing them in wasn't a problem. In fact we were given previously owned seaboot socks to go with them. We also found that an ancient anorak could be re-waterproofed by careful application of the ubiquitous shiny black 'Bodge tape'.
New boots? You've all gone soft, so you have!