my suggestion would be to take the middle shelf out on the top row - put a larger picture there or a pretty colorful vase. Try not to over crowd it - add some matching baskets - Target has some cute ones in the ITSO collection. If you want it to look full without being crowded try adding some fun scrap booking papers attached with glue dots to the back (less permanent than wall paper but same idea). If you put pictures in there - make sure they all match in tone (like all black and white or all colored). Big block letters are fun too! And vintage books are a great way to fill up cabinets.

First of all, feel free to leave some shelves bare.You seem only to have room for a single piece per shelf in much of the case, so I suggest gathering photos, and anything you own that you would like to showcase, as well as items you might use for 'lifts'.

Here are a couple of ideabooks that might help:
http://www.houzz.com/ideabooks/9874/list/How-to-Arrange-Shelves-with-Style
https://www.houzz.com/magazine/11-styling-tips-for-shelves-youll-love-stsetivw-vs~490100