My 5 tips:
The Kunstmuseum Den Haag by the famous architect Berlage. A wonderful example of Dutch architecture and a great art collection.
The Denneweg is a world famous street in The Hague for going out for a meal. Highly recommended. I love Indonesian food myself, with the Soeboer restaurant on Brouwersgracht as my favourite.
The Papaverhof from 'De Stijl' architect Jan Wils from the 1920's in the Bloemenbuurt. Still beautiful and modern, but also intimate and tranquil.