Hi,there!
I have a son who will be 3 in May and we started Potty training officially on his 2nd birthday, but he definitely showed signs of readiness around 19 or 20 months. I just wasn't in a position to do it right, so I waited a few more months until I could commit to it.
He mastered the potty during the day quite some time ago, but I kept him in pull-ups at night until he mastered that, and just last night, he told me he was a "big boy" and that he doesn't need them anymore. I told him that if he woke up this morning with a dry pull-up, we would throw them all away. Lo and behold, he meant what he said. Dry pull-up this morning, he's done with them.
As for initiating the process, the two main things to remember are consistency and commitment. Once you start them on this road, you can't wimp out when it gets inconvenient. If you just stick it out and commit to a die-hard training process, you can see incredible results in just two weeks.
Make sure that once you decide to start it, you can commit the time and the effort to it for at least two straight (messy) weeks! Do NOT flip flop between underwear and pull-ups during the day. Pull ups should ONLY be for night because they keep the children from feeling the wetness they need to feel when they didn't quite make it to the bathroom. That feeling of "uh-oh" is part of the learning process. By denying them that, you prolong the process, and don't allow them to come to the conclusion that they need to go when they feel a possible "uh-oh" moment coming on. Failure is an important part of success!
So decide on the time when YOU are ready... people think it's the child who needs to be ready, but really, parents postpone potty training because of the inconvenience it causes THEM.
Then make a schedule, and take them to the potty every day at the same times come hell or high water. (When they first awake, right to the potty. About an hour and a half later, to the potty. Then about every two hours, right to the potty).
They are bound to have to potty at one of these intervals, and when they do and they succeed, it breeds more success. So by taking them consistently and frequently, it increases their chance at success, and it just clicks. They see that they CAN do it, and then they start doing it.
For that two weeks straight, don't deviate from your scheduled potty breaks. That means you have to think ahead when you go to the store, when you go shopping, when you go out to dinner. You can't sluff off at these times, you have to stay on schedule and stay vigilant and anticipate their need to go before they do, and position them for success by making sure that they are not in a place or position where it makes it difficult to go when they need to.
Lastly, talk about it all the week before leading up to the big start date. Talk about how you all are going to start going to the potty and help them to anticipate the two weeks. Get a potty book and read it to them once a day leading up to the big two week commitment. Let them go to the bathroom with their dad and see how it's done. Then the day before the big event, go and make a big deal out of letting them choose their "big boy" underwear. And then once you put them on, don't take them off unless they are going down for the night.
And oh yes, during this time, be careful to decrease their fluid intake at one sitting. Don't fill their bladders too much at one sitting to the point that it makes it difficult to hold their urine until the next potty break. Again, help create an environment for success.
After that two weeks of die-hard routine, keep the schedule, keep taking them frequently and ideally, they will have adjusted to the routine and will kind of anticipate going to the bathroom and hopefully make the connection between asking and going. Even if that comes later, the point is that they are learning to hold it and control their bladder until they have an opportunity to put it in the toilet and not in their pants.
I know that this was very long, but I hope that it helps.
Best Wishes!