Somebody gave me a great tip which worked really well with my son when he was learning.
Put a toy plastic golf ball in the toilet (the type that has holes in it and will float rather than be flushed away each time) and tell him to aim at it when he goes. As well as being a great game it means most of the wee does go into the loo.
Hmmmm, I wonder if I should reinstate this again now he's six and it still ends up on the floor ?