Start with the practical list
I’d start with leaks, lingering humidity, poor lighting, weak storage and anything that’s difficult to clean. Solving those problems helps the finished bathroom feel good to use.
Check what is behind the pretty parts
Ventilation, plumbing and electrical work can change the ceiling or walls. I want those questions answered before falling in love with a particular fixture or finish.
Then have fun with it
Once the practical plan is settled, choose the vanity, mirror, lighting and wall color. The decorative choices become much easier after the repair work is complete.