For me, the best way to break them in faster and to make them less painful was to just wear them. The more I wore them, the softer they became. One thing that really helps is to heat them up a little bit before putting them on with a small heater or fan, just enough to soften the rubber a little bit, not too much though to not damage the shoes.
Another thing that really helps and that is very simple to do is to just bend, twist, and fold the shoes for a minute or two. This really softens up the rubber and makes it much easier to put on and less painful to wear.
Honestly, getting the right size and just wearing them will really get the job done.
If your shoes are just not the right size though, then it maybe either not get better, or it may be a very long process. Not being the right size also includes shoes that are too big, so keep that in mind.
One thing I like to do is to bend then around and scrunch them up before putting them on. I do this for about a minute and it really helps soften then up and makes them much less painful.
