They spend a lot of time in there rooms...
So make sure that they love their rooms and they are surrounded by things they love!
Their bed has lots of pillows for them to chill, also to disguise the fact that they haven't made their bed!
They have a really comfy bed, lord knows they sleep a lot!
Because they spend a lot of time in there make sure they have a good desk, chair for study (or Facebook...)!
They are messy!
I guess that maybe the design of their room is a bit "relaxed" so it looks like its meant to be a little messy!
Their clothes/shoes/jewellery/bags/make-up is everywhere...
Again, storage boxes/containers/cupboards... every little bit helps... and if it can be designer (ie Tiffany/Hermes/Chanel packaging!), bonus... as no doubt it will be on Facebook/instagram/tumblr!