you have to figure it out by yourself. the way you like it, you feel comfortable.
when you have some spare time smoke some mindexpander, throw in a nice CD you are in the mood for and design your room as you want.
i personally like my rooms with lot of colors, i have many psychedelic backdrops on my walls and other fluorescent decos that glow under UV light. i also like lamps, have many of them too, hidden behind my stereo, a lightutbe under my sofa, lavalamp, and some other ones here and there. i also have a big seat cushion and a nice carpet to sit on the floor. some small tabel to put things on. and many many small gadgets and toys to play with when listening to music, chilling, hanging out with friends. i would also recommend plants and candles. a good tip i think is to put away electronic devices like laptop, tv etc. they are really disturbing when chilling. if you like you can put some personal photos of friends, trips etc on the walls, wardrobe etc
its all up to you and your imagination )