I was really consistent when it comes to taking him. I did every hour or two until he made a pee or poop and keep doing that. As for poops, my son is pretty predictable when it comes to poops, usually about 15 to 30 minutes after eating and mid morning. I would take him to sit on the potty around his poop time and have him sit for 5 minutes and do that every 15 minutes or so and sooner or later he had to poop and did so. It took a few days but eventually it worked. I also constantly reminded him he was wearing underpants and he couldn't go potty in them. It took a good 3 weeks to a month before he was pretty much accident free.
I tried this when my daughter was able to sit on the potty seat by herself with out falling in to the toilet(they will get scared if they fall at least one time and it will be harder for them to recuperate from that fall)she was 1 yr.1/2 but i would do it every 30 min. It was tiring but she got used to i saved lot's of money on diapers.I also tried it on my son .It works the same for boys and girls if you do as what Jessica said Consistent Schedule and always tell them they did a great Job Big Boy or Girl and give them a high five they will know it's serious .This really works trust me you'll have a diaper free toddler by the time they turn 2 yr. old.
I sat my child on the toilet, BACKWARDS, boys and girls, on the hour, every hour. Sitting backwards they can see what they are doing, and can hang onto the toilet seat or lid, feeling secure. Along with this, I had them hold their arms close to the sides of their bodies, make a fist with their hands, and make a growling sound like a bear would. This automatically gives them a "push" feeling. This method works very well, and with playing "bear" makes it fun at the same time. Donna