Best ways to see it: day cruise (Mitre Peak, Stirling Falls, fur seal colony), overnight cruise (Real NZ or Fiordland Discovery), scenic flight from Queenstown (45 min each way, weather dependent), or kayaking with Roscos Milford Kayaks.
Practical tips: drive yourself from Te Anau (the road through Homer Tunnel is one of NZ's great drives), or take a coach from Queenstown for a 13-hour day. Fuel up in Te Anau - no service stations in the park.
When to go: Dec-Mar has the most stable weather; Apr-Oct is quieter and gets the best waterfall conditions after rain.