I read that Gertrude Jekyll, in her garden designs, worked toward the appearance of plants having occurred in that arrangement naturally. That is exactly the "look" I love most in the garden, but have found that it requires considerably more thought and planning than one might think. I've never been good at detailed planning on paper, other than listing plants I'd like to grow together.
Seems the Cottage Gardener must toss a lot of standard garden advice to the wind, like "tall plants in the back, short ones in the front". In the casual Cottage Garden, I love the look of shorter clumps of blooms, peaking from behind a taller plant, beckoning the onlooker to come see what lies in store. The very nature of gardening implies the constant need to move plants around in an effort for them to marry well with their companions. Like marriages among people, some don't last, some are great for a while, till one outgrows the other, and a select few stand the test of time.
Unlike the traditional Cottage Garden, my gardens meander around 5 acres of lawn space, in amoebic shaped (...or would that be shapeless?) beds with serpentine borders that follow the lay of the land. There were already a lot of mature trees dotting the landscape here when we moved in, most of which were well positioned (thankfully!).