When you live in a small apartment it's really hard to decorate. The real estate is really important. So you never want huge pieces, but you also don't want to go super small. Some people think that when you have a small room you go with really small pieces.
A really nice sofa will make a space feel and appear larger and you want to be comfortable. You never want your larger guests or if you're a taller person, sitting in a really small little chair. So your sofa you can go regular size. Make sure that it's nice and comfortable for you.
But the rest of your furniture you want it to work double duty for you. So if it's a table, maybe it pulls up into a dining table. If it's a side table, make sure that it has storage, so you can put all your books and things away. If it's a TV unit, make sure it has drawers and lots of storage. Storage is really important in small spaces so you just want to pay attention to that.
Also the rule that dark colors make a space appear smaller is not really true. So go with the darker colors, just make sure to balance them. So if you love a navy blue or you love a deep red, go for it. Just make sure then, that you also don't have a dark sofa and a dark carpet. It's all about balance here and it's all about making sure that your furniture works double duty for you.