Sedums are wonderful plants to use in most gardens. As with most perennials, plant them in groups of three or five or even larger drifts. They are attractive and offer interest all year so use them as a key repeat plant.
They associate well with grasses. One of my favourite combinations is to use the small whispy grass called Stipa tenuissima with Sedums. They also look good with other autumn performers like asters or the blue flowers of the shrub Ceratostigma willmottianum. I love the low growing Sedums as well and the grass Pennisetum draped over the Sedum 'Ruby Glow' looks gorgeous.
Try textural contrasts - the cool leaves of a Sedum against the furry leaves of Stachys byzantina or the delicate filigree of Artemisia. Or try small Sedum leaves against the big, fat leaves of a Bergenia.
Here is a combination I love -
Phlomis russeliana in the background with the grass Carex comans 'Bronze' and Sedum telephium 'Matrona' in the foreground.