Start off on grass instead - treadmills make you run differently which is against the point of running barefoot. I'd start off with 5-10 minutes and build it from there.
If you've got sports pitches / a park near home then you can just tag it on to the end of your normal runs.
Start off increasing by 1 minute a week or 1 minute a fortnight, but after a while you'll be able to increase the rate of increase as you get more used to it.
If you're transitioning from shoes with a lot of drop there'll be a lot of extra strain on your calves and achilles - do plenty of stretching and strengthening - calf raises standing on a step are good as they put it through the full range of movement
At Dal we would do barefoot strides on the artificial turf about once a week. Really great training, could feel it stretching out your foot muscles.
But as you say, easing into it is important.
Okay I'll use the turf soccer field we have here! Thanks :)
Pardon my ignorance, but what is the purpose of barefoot running?
It help reduce running on your heels which is not natural and is the cause of many running injuries. Running barefoot strengthens the muscles that are not used in running with shoes so that your body can run more naturally and smoothly
Does it work if you run barefoot in sand (ie, a beach), or only on a firm surface?
Maybe not as much on sand because quiet a few motions would be exaggerated. You would get a different benefit from running through sand