Weather-wise, the Netherlands is similar to a lot of countries in north-west Europe. The country experiences warm summers and cool winters, though temperatures usually never fall below 3°C.
You should plan your trip based on specific events that you want to experience, rather than what the weather will be like, as there are things happening all throughout the year. June-August are naturally when the country receives the most tourists, but March-April is also a great time to visit due to the plethora of events on show, such as Kings Day.