Get a Jungfrau Travel Pass. 60% of the experience here is riding the beautiful mountain infrastructure — it's expensive, but totally worth it. With the pass you ride it all unlimited, so get the three-day pass and use it liberally.
Have lunch at a mountain lodge. A lodge high up in the mountains is its own amazing experience worth planning around — they're often right at the train or gondola stations and built into the hikes, usually with playgrounds and beautiful views. (Look for the lodge icons on the map.)
Expect crowds — but only in the obvious places. You're visiting one of the most popular corners of Europe in peak season, so the villages (especially Grindelwald) and the big transport journeys will be packed with tour groups. The good news: the moment you actually start hiking, the crowds thin out big time.
Download the trails offline first. I'd save every AllTrails hike to your phone before you head up — signal gets patchy on the mountain, and you'll want the route in your pocket.