There is only one hard and fast rule when it comes to creating a garden and that is right plant, right place. This means that if you want the plant to flourish you must be sure that it gets the light and water that it needs, plus the soil that you plant it in is able to provide the food the plant needs.

Other than that your garden is a reflection of you; so toss away all the other rules and have some fun. Mix colours and sizes if that pleases you. You do not have to plant a garden in a straight line or inside a bo x, circles, ovals and figure 8s will work as well if not better.
There is one other element to being a happy gardener and that is : make sure your lifestyle matches the garden you wish to have. 

If you have only a few spare minutes a day, do not plant a garden that requires constant attention. go for native plants that can, for the most part, look after themselves once they are in place. Keep the garden small , perhaps a container or three.

photo: courtesy aussegall/flickr.