Perhaps the easiest way is to choose a colour scheme
What about cool and restful. Shades of blue, lavender, white and green

begonia petunia bacopa geranium petunia bacopa cool spillers shades of white petunia mix bacopa verbena bacopa bacopa cool fillers geranium petunia & bacopa cool spillers verbena & cineraria petunia mix petunia verbena & callibrachoa
What about a hot fiery mix, reds oranges and strong purples

hot fillers hot spillers coleus begonia bidens coleus begonia bidens begonia marigold bidens marigold petunia canna begonia bidens canna petunia mix begonia cameleon petunia red & purple warm pinks petunia verbena contrasting colours petunia & bacopia geranium fuchsia & lobelia begonia begonia big petunia & bidens verbena petunia & bidens Hot foliage begonia pendula begonia boliviensis hot foliage and flowers
Are you a frustrated designer, do you have an eye for colour and fashion.
Making a planter or hanging basket, allows you to develop your designing skills, on a small scale. You can move plants around to find the best combinations, play with textures and change colours.
A planter will allow you to test colour combinations and shapes, unlike home furnishings or paint, plants change shape and colour as they grow, the possibilities are limitless.