Rhododendrons prefer a cool spot in the garden with dappled shade, although they will tolerate full sun as long as they are kept moist during dry spells, a general rule is that the smaller the leaf the more sun tolerant the bush will be.
These flowering beauties like to grow in acidic, free draining soil, they are shallow rooters and can even be grown on top of the soil in a good mound of mulch if your soil is not free draining. Good mulches to use are pine needles (these are great because they are acidic), pea straw put on a thick layer and replace every two years, and bark, all are great for inhibiting weeds.
If you have good drainage and are planting your rhododendron into the soil, dig your hole twice as big as the root ball, mix in compost with the soil and back fill gently, do not stomp down the soil with your feet as you may damage the delicate shallow root system. Finish with a mulch to retain moisture and keep down the weeds.

Care

Avoid weeding and cultivating too deep close to rhododendrons because it is easy to damage the fine roots of the plant, instead gentle hand weeding is recommended and mulch to help stop weeds reappearing.
Trim spent flower heads to encourage new growth and next season flower production rather than producing seed.
Fertilize rhododendrons in spring, apply around the drip line of the bush and water in well.