Having just renovated our living room at home, I am well aware of how hard it can be to style a shelf! It's always a balance between making it interesting and knowing when to stop. I don't believe it has to cost the earth either, in fact most of the things I used on my shelves were already in the house, just hidden away.
My biggest tip is to add all the things that mean something to you personally, whether it is a trinket you have picked up on your travels or a family heirloom. Anything special to you that you want to display.
Amongst my precious items are a painting of Edinburgh given to me by a dear friend for my wedding (many years ago), some vintage Flower Fairy books handed down to me from my Aunt, and a candle holder made by one of my girls in tech! No matter what these things are, they will all come together beautifully to tell a story about you and your family and nothing matters more than that when you are creating your home.
My Pinterest board on styling a shelf has lots of clever, expert ideas on how to group items and some gorgeous inspiration.