This is one of the easiest rooms to start with. If you own, (not rent), first thing i would do is paint the oak vanity. It doesnt go with the gray floors. What colors do you like? Pick out a shower curtain you like, pull a color out of that for your bath rugs, the rest will fall in to place. What color is your master bedding? Maybe start with a color in there that you like and carry it in to the bathroom?

Since you rent, I’m assuming you can’t paint anything... so I’d start with a colorful shower curtain and then go from there with towels and other accessories.

shower curtain click on the link for an aqua shade to perk up the nice bathroom. Here's a photo of one that would work and then I would add fluffy white towels. I'd also like to see something in between the two sinks and some art on the wall. https://www.bedbathandbeyond.com/store/product/dkny-highline-stripe-shower-curtain/3281080?keyword=white-and-aqua-shower-curtain