When I ran my first Marathon I did 15m 6 weeks before followed by my first official half marathon (English Half in Warrington) followed by a 15.5m, 17.5m and a 19.5m in succesive weekends and then a weekend off before the big event!
Totally disagree about water. Cups are worse than useless unless you are willing to stop to drink, which most people aren't. We had a banana at end which is the best food we could have to refuel. Baggage buses were 50m from finish line so if people wanted food immediately afterwards they could have brought it with them!
I think that people suggesting things like more toilets (never seen so many) foil blankets and energy drinks at half way (both of which you rarely see at a half marathon) shows just how fantastic and faultless this run was!