I used to walk around the house with mine on.
Walk a lot of stairs or ride a bicycle with them.
Walk around in them for a couple hours for like a week or less, it depends and oil them and do whatever you can to stretch the leather a little. I found that putting the tips of my toes on the bottom stair and lowering my heel helps too.
Leather oil...but a lot of it. Then put them in the sun. Makes the leather soft and they don't blister you as bad.
Oil them, wet some newspapers and stuff the boots with them. Leave overnight, take out the newspaper and let (air!)dry . It always works for me!
Wearing them in the house and oil them all the time!