CONSISTANCY!! At 2 and 3 they like to see progress. Individual potty sticker charts are always good. Having a cheap toy out of reach that they get to have after a certain amount of stickers always works well also. My son would pick out a toy from the dollar store, when he got 10 pee pottys or 5 poop potties, he got the toy along with a sticker of his choice on his potty chart. I have done this will several kids I nanny for, and seems to work the best. Good luck!
You know what I finally did! I got my child some pullups and put those on over the top of the underwear I let him choose, so he could feel when he went pee and get wet and uncomfortable. Then I set the timer for every 15 minutes after he peed, so I could catch him the next time. I put him on the toilet every 15minutes for at least 2minutes each time until he went! Gave him one M&M when he went and got all excited and made a big deal about it! Do not give him or her an M&M if they do not go or you will not get any results!!!! :0)