Get as much information about the girl as possible before beginning. Though not all of it may seem useful, any shred of information can help.
[header] How to make a very modern room for a teen girl inexpensively [title] Take the girl's tastes into consideration. [step] Though you may assume all teenage girls appreciate similar things, you could be drastically wrong. Ask her what favorite colors, bands, celebrities, hobbies, patterns, and room styles are.