I followed the advice from Dr Christopher Green in "Toddler Taming" there he says to buy terry towelling pants and let them run around in them, when they wet the wind comes down from the hills and freezes their little botts and now they understand the meaning of wet. After that whenever I went to the toilet she was put on the potty, after a drink, and if it had been a while. If she went she got praised if she stayed she was praised and if she had an accident then she was changed without a fuss, given a kiss and told to go play again.

By 3 my nephews were 3.5 and 4.5 and the older one would encourage her to go potty and praise her up if she did something and bring her to me for changing if she soiled herself. She got it with time but then came the urgency where she was engrossed with something and didnt realise she had to go until she nearly wet herself and on the way to the toilet didnt quite make it.

Children will let you know when they are ready but 3 is about the time they can understand the signals.

There are LOADS of articles on potty training on Minti - just search in the "find it" box top right of the screen. Also, I liked the approach on this lady's website (though I didnt buy the book!) and like this "readiness quiz" she has.

Do your background reading, decide if your son is at all interested and if not, take some steps to slowly get his interest - you are going to have to start talking about what is going on with him and others in the house, so he starts to recognise the words that go along with toilet training; if you can bear to, leave the toilet door open so he can observe; buy a potty and leave it in the living room so he gets used to it (and let him sit on it fully clothed if he wants to use it as a chair for now); and if you have friends with children slightly older (say +12 months) invite them round so he can see what he will be doing in a year or two from now (my DD1 gave up using the potty and toilet insert seat after observing that her two friends, 11 & 20 months older, did not use either when they went to the toilet).

Dont stress about it, he is still little, and most boys seem happier to train nearer to 3 so you havent got to start tomorrow. Take your time! Good luck!

 have a look  here at my answer to another similar Q.   It explans how we started to train my now 2 year old son.  

my son's potty training started when he started to take an interest in what daddy was doing on the toilet. we bought him his own, and whenever we got the hint that he would be going to do #1 or #2, we sat him on his potty asap. it takes a while. u have to catch them starting to do it and pick them up and sit them down faaaast! then the rewards (stickers) and everyone making a really big deal (brothers, sisters, grandparents)