Hi there - not an expert as DS 3.4 is not yet trained but I have read lots of books and threads on the subject
Preparation stage: buy a potty, talk about what it is for, read a story book about potty training, let them practice sitting on it, take them to the loo with you for demonstrations, buy some exciting pants, sit teddy on the potty, sit dc on the potty at nappy change and bath time
There are various schools of thought but all say wait until the child is ready - defined in different ways, - can say when they need to go, can say when they have been, can undress, aged at least 18 months, can follow instructions and concentrate on one thing of a reasonable length of time,
- boot camp aka Gina Ford (quite a good little book) Stay at home for a few days - straight to pants potty every 15 min for the first day (yes really!) bribes for successes, never mind type noises for accidents and it should all be sorted in a week
- gently gently approach, the no cry potty training solution - keep nappies on but encourage dc to use the potty when they need to go - use pull ups. Generally this method is frowned on on MN - confusing.
- Child led potty training - wait until the child says - I don't want to wear nappies any more mummy. say - ok then and buy them some pants. Apparently this method has instant sucess but you do have to wait and it might be until dc is nearly 4 (but I know at least one just 2 year old who did it this way).
I quite like the NCT potty training book too.
Personally I would wait until dc is showing enthusiasm and has weed on the potty or toilet purposefully a few times - save yourself too much in the way of puddles and misery.
Good luck