I think there are a high number of duds in the fruit but they are slow sprouters and growers, of that there can be no doubt.
A lot of sites and books recommend piercing the stone with cocktail sticks and suspending so that the broader end is in water. I personally have not had any luck with this method after three or four attempts- they just went brown and rank.
What worked for me last time was planting the stone in a pot of compost so about 1/3 of it was above the surface, watering well and placing the whole in a clear plastic bag (with the top loosely open) somewhere fairly warm. It was checked once a week and if dry watered.
Very, very slowly (this was winter which probably made matters worse) a shoot started to emerge. I wasn't sure if it was a root or a shoot and dug up and reburied it a few times in different orientations which can't have helped.
When left properly alone for about a month the shoot poked its head above the surface and fairly rapidly (for an avocado anyway) grew proper leaves and is now about six inches high with three sets of big waxy leaves.
Maybe you should get three or four stones on the go in pots and see if any of them work out? I think the shoot will emerge much faster at this time of year than in winter when I started mine off. They seem to like being left well alone for about 99% of the time so avoid overwatering and resist the temptation to go poking around in the compost.