I've just abandoned the dummy for my DS3. I'm not cruel, it was just that it was interfering with BF. He's nearly 8 months.
Before then, he would go off really quickly with his dummy.
Now we often have to do lots of feeding or rocking/humming.
But just lately, when he's had a good feed, I've put him in his cot and twice he's gone off to sleep by himself with a little bit of muttering and singing.
I've been putting him in his cot for a bit when he's tired but in a good mood to get him used to it too - that seems to be helping.
I plan to gradually get him used to longer and longer periods in his cot. I will try rocking for a bit longer and putting him down when he's really drowsy but not quite asleep. If he cries, I'll pick him up again. i think there is an optimum point actually that you have to work out - when they're almost asleep but not quite but ready to go on their own. But it takes a bit of practice.
Then when we've cracked this for a few weeks/months, i imagine he'll get happier just going down by himself a bit more.
But I don't expect miracles - the 3 year old still needs lots of cuddles and toing and froing to get to sleep.