this worked for my 3 year old charge:
this is what we did when my 3 year old turned 3 (from being 2, having been trained since 22 months)
If watching TV (they have sky+) the TV was always paused for her to go to loo. If she had an accident she missed the programme
then as well as all the praise etc for going to the loo...
If she had an accident the following happened:
She IMMEDIATELY had to walk herself into the toilet (no 1 more play, just doing this etc) in the toilet she had to remove her clothes HERSELF...
then she had to sit on the loo and try to do some 'more'
then she had to carry her clothes HERSELF and put them in the laundry basket...
then she had to go into her room and put on the clothes that I chose for her (she LOVES choosing her outfits / clothes etc and having pink pants and charachter pants etc) so she did NOT choose her clothes
(I chose for her the plainest most boring of knickers (ideally plain white) and appropriate clothes that were NOT her favourites.
She then had to put these clothes on HERSELF (she had help with really tricky bits, but otehr wise had to do it her self (+ quite slow and boring when u are 3 ) She then had to go back into the toilet and wash her hands....
then life continued as normal...
basically by wetting herself she still had to have the 'trouble' of going to the loo, and washing her hands etc.... but she also missed out on any fun for several minutes while she undressed and dressed her self etc.
Within less than a week she had stopped having accidents!
Good Luck
(also while she was changing etc converstaion was just minmul, ie take off your trousers, put them in the wash bin, heres some more socks for YOU to put on YOURSELF etc... none of "oh isnt it raining hard at the moment lol")