These trees secrete juglone, a hormone supposedly toxic to rhododendrons and members of the nightshade family. Prepare the planting hole as you would for any tree or shrub. Azaleas are shallow-rooted, so dig it no deeper that a foot and twice as wide as the rootball. If you've bought your azalea from a local nursery then set your plant an inch shallower than it was growing in the pot. Mulch the planted azalea to retain moisture, but avoid heavy mulch, as it will deprive the roots of necessary oxygen.
Wood chips make excellent mulch and help keep the pH low.
Do not amend the soil other than adjusting for pH. Research has found that adding fertilizers and compost to the planting hole encourages roots to stay in the hole, rather than reaching out for nutrients. This provides a poor support for the plant. Fertilize your azalea in the spring of the second year. Hardy azaleas, just like their indoor cousins, need lot of moisture. One reason mine has done so well over the years is that it's planted in moist, high organic soil.