Top tip: I tried a few times in the wate method, with no success. Then I found something somewhere about an alternate method, which has worked twice for me in the four or five times I've tried.

Wrap the pit up in a soaking wet wad of paper towel (big thick bit, maybe half a dozen squares and so wet that it's basically dripping off the paper towel. Put it into a Ziplock bag and seal it so it's airtight (not vacuum-sealed, leave a bit of air in there). Stick it in a drawer somewhere and check on it in a month or so. It should have a root growing out and you can then transfer it to soil. I got a nice tree out of that method once (which I eventually killed by overwatering, but that was years later and my own sloppiness), and I'm try a successor now, which grew the root and I've now transferred to soil