We are trying with my three year old right now. This is what we are currently doing, after I looked some stuff up on the internet.
He will not go on the pot on his own, and gives us some problems about it when we ask. Of late, we are having some progress using "incentives" and "disincentives", and putting the requirement to potty train on someone else -- the doctor.
My son recently had a doctor's visit where the doctor told us we have to get serious about potty training. He remembered that. So, I told him that the doctor called me to ask how he was doing, and I said he'll go sometimes. The doctor told me that is not good enough, and that we need to use the chart. (You can find free incentive charts online.) I have one with a boy on a bike, and a house on the end. There are five arrows leading to boxes, each box is a reward, when you get to the house, it is a bigger reward. We asked him what he wants. (You can modify the request to something small.) He told us he wants cars, so one Matchbox for the first box. We were in an ice cream store the other day, he wanted a clown cone. That will be another box. He colors in an arrow each time he goes. The house will be dinner at McDonald's. You can do whatever, but it has to be something that they want, or it's not an incentive, that's why we asked him what he wanted.
Now, he's not going on the pot with that much more frequency or prodding from us, but he is going more willingly, and when he goes, he says very excitedly, "We can tell the doctor!" He likes filling out the arrows, and he talks about his rewards a lot.
If he goes in his diaper, we take something away for fifteen minutes, and time it. Putting the blame on the doctor has taken some of the fight away. The last time I had to take his cars away, he cried, but he gave me the cars, which he previously would not have done if he perceived me as having the power. He would have run away, or fought my taking the cars. So, there have been some changes. The disincentive, I've found, should be something that they are doing or want immediately. (Heading out the door -- no music in the car, you are outside -- no riding of the whatever.) They need immediate connections between behavior and disincentive. I said, I know, I am so sorry that you can't play with your cars, but that is what the doctor says. You try to be on their side, and you say, that's ok, you'll do better and remember next time, I know you can. You are not supposed to get angry.
In a few weeks, I will tell him that the doctor said no more diapers, and we will move to doing a potty training cold over the weekend, using many of the suggestions already given here by various ladies. (Keeping potty handy, etc.) just putting him on the pot and either bare bottomed or big boy pants. He wants Spiderman pants, so I might tell him he can wear them to school on Monday, depending on how well he does over the weekend.
So, I am going with a more gradual approach. My guy goes pretty willingly at daycare, but is still not asking to go there. At home, he was just fighting us. So, a power struggle was going on with us, and we had to shift the power to the doctor. It is going fairly well. I expect that it is going to be a long haul with him, he just doesn't care about being stinky or anything. But, he barely fits into the diapers, his diapers are just too gross to change, so I've decided we are going to push it a bit. The trend now seems to be to let them do it at their own pace, but I can't do that anymore. So, I might have more trouble than if I waited to let him come into it on his own, but I might get him to do it faster.
Good luck!
Oh Jeez, I just read the post with the lady with the three year old and the doctor telling her it was time to go. The advice I read said kids over three are capable of going, if they are not, they are typically in a power struggle with mom or dad. I wonder if that is what is going on with her little girl!