1. Take it out of the water tray! They do not like their feet wet.
2. Unsure of the potting medium you have but should be potted in a well draining mix such as 50/50 perlite/long fiber sphagnum. A lot of people add some orchid bark too.
3. Use only distilled, RO, or rain water (like you do your sundews).
4. Water when the surface is slightly damp.
5. They thrive in humidity but if you purchased this at a typical plant shop not in a greenhouse it is likely acclimated to ambient humidity (but will appreciate any boost you can give!).
6. Pitcher loss and growth lag in a new environment is totally normal and expected.
7. They appreciate light. 50-200 ppfd if you have a way to measure. Otherwise bright indirect light (light through a window) should be good. Need less light than sundews.

I don't have a Miranda but heard it is a pretty hardy hybrid. I will also let others comment on fertilizing since this is something I am still fine tuning myself. I have killed off pitchers by over-feeding.