Hi M.
I have a 2 year old daughter and a 5 year old daughter. Whilst I realise it's probably different to potty train girls and boys, I thought I'd tell you what has worked for me...
When you make the decision to potty train, you have to DO IT. So you take the nappies off, and put your child in underwear and that's it. There's no going back. Obviously they will wear nappies through the night until they've mastered the daytime dryness, but if you flit between nappies and underwear during they day, it creates confusion and 'accidents'.
I'm on Week 2 of potty training my daughter, and so far she's doing great. There are no nappies during the day, only for sleep times (she sometimes naps at nursery for half an hour, so they put a nappy on her for that, but she understands nappies are for sleeping).
The other thing I do is ask her to sit on the potty, rather than ask her whether she wants to use it. So I get her to sit on it every hour or so (depending on what she's drinking!) and that way, she will get used to sitting there, sometimes peeing and sometimes not. The important thing is that when she DOES pee, it is on the potty nine times out of ten. Now on week 2, she tells me when she's going to the potty, as well as me asking her to go and sit on it. Eventually I'll stop asking her and she'll tell me more and more....
Good luck!
C. x