Adding well-thought out ornamental & structural features to a garden are what transforms a well-designed, well-planted garden into a space with "atmospheric magic" (that can be a term, right?); it helps make the garden come alive with personality!
When picking out features to add to your garden, consider the style of your garden. Is it more formal or informal? Choose features to complement your space & create a unified look to avoid confusion. For example, a garden gnome, in most cases, would look out of place when placed across from a large stone Buddha. Whether you are going for a style that's Zen, shabby chic, country, or whimsical- try to keep it streamlined enough to avoid clashing & create an overall cohesive look. With that said, there's no reason to be boring- there are some really creative, unique garden statues out there these days! Finding one (or a few!) that speaks to you will help your personality & your garden's personality shine through in your landscape.
Creating height is something to always consider when embellishing a garden. Varying heights, like in interiors, creates interest in a garden. Another way to add height (besides, of course, using trees) is thru use of structures such as pergolas, trellises, gazebos, & obelisks. These structures, like statues, also give your garden personality & many of them add a functionality to your space as well. Adding an element like this adds another layer to your garden & therefore enhances its personality & interest.
To introduce a completely different element into the garden, consider adding a water feature. It moves, creates sounds, & reflects its surroundings. Water also encourages wildlife such as frogs, birds, & butterflies. And here's a fun little fact: if you want to attract butterflies in a simple way, add some larger rocks to your landscape. Find rocks that have some crevices & when it rains, the water will slightly puddle there. Butterflies love those tiny puddles- they will use your rocks to perch on & get a drink!
Making a statement: The general rule of thumb of less is more can be applied, but also remember, this is your garden & your statement to make! When in doubt, keep it simple. The important part to remember is any element should complement your garden, not distract from it.