Perk up hanging baskets

When you see those huge, tumbling, beautifully-flowering hanging baskets in open gardens, outside pubs or strung up on lamp posts through summer,
for gardeners it's always with an envious eye that we look at them. How on earth do they get to be so teeming with flowers and foliage and looking so perfect? The key to their success is constant care, more so than with standard container planting.