A successful hanging basket is a voluminous profusion of trailing and flopping plants. Plants should burst out from the underside of the basket, unless you are a fan of the upside-down bald-pated look.
Therefore, avoid moulded paper liners, which are difficult to insert plants through. And avoid sphagnum moss - as used in the photograph above - unless you can be sure that it has not been removed from a bog, or other important habitat. Instead, try a recycled wool liner, or make your own, if you happen to have an old green or brown jumper (the plants will soon camouflage it!).
To fill the basket, cradle it on a large flower pot, or bucket. Put in the liner, and then an inner liner made from a piece of polythene cut from a compost bag (to help retain water). Make slits in the sides, to accommodate plants.
Put in a layer of compost (a mix of half John Innes no. 3 and half multipurpose), and insert trailing plants through the slits. Add more compost, and more plants. Top off with some non-trailing, but low-growing plants (most fairly compact bedding plants are suitable).
Water at least once a day, and feed and deadhead regularly.
A simple colour scheme of one or two related colours is more effective than a jangly confection that ranges across the spectrum.
Trailing and flopping plants include: bacopa, bidens, convolvulus, diascia, fuchsia, geranium, helichrysum, lobelia, lysimachia, nasturtium, nemesia, petunia, verbena.