1) group objects together in odd numbers - even numbers makes things look awkward
2) fresh flowers make any grouping of accessories pop (as you'll see in just about every image in this post)
3) stagger similar sized objects at different heights - objects placed on stacked books is a good way to do so
4) group together several of the same accessories together for a dramatic effect (ex: the coke bottles below and the purple bottles toward the bottom of this post)
5) when accessorizing bookshelves or a mantle, mix it up with objects and accessories in all different shapes and sizes - this will make the overall look feel balanced when completed
6) don't group together lots of little accessories (unless you're going for the "tchotchke central" look)
7) mix different textures and materials together, such as raw natural wood with colorful porcelain, or metal and glass...makes things much more interesting!
8) Edit, edit, edit! Know when to add or subtract pieces to get it just right :)