4) Ammend poor soil. If you live where the soil is very high in peat, pure sand and gravel, or limestone, consider digging out a hole about three feet in diameter and two feet deep and planting the rose in that hole. Use imported 'rose soil' in the hole. Most people, however, can add things to improve the soil. Gypsum will loosen heavy clays; so will compost. Lime will help neutralize acid soils. Sandy soils can be made usable by adding lots of compost.
In ammending soil, keep in mind that where there are abrupt changes in soil composition, most plants will not send new roots across the boundary, so if the soil in a hole is markedly different than the surrounding soil, create a zone in which the two are evenly mixed to help the roots make a transition into the surrounding soil.
It is a good idea to have your soil tested. It is not unusual for soil to be 'pretty good' in most aspects, but severly lacking in just one or two. Targeting the weak spots is the most effective path to good soil. In almost every location in the US the addition of organic matter (compost, etc) will be the most important step in improving soil fertility
5) Get ample water. If you live in a place that suffers frequent droughts, consider placing a rose where it will get extra water. I once planted a New Dawn rose at the outlet of a downspout in Texas, and the rose grew 24 ft in each direction in one season. Remember that climbers placed under the eaves of a house may not get as much rain as the rest of the environment, so they will frequently need extra water.
An inch of water per week is considered the minimal amount for plant maintenance. In unusually hot weather and growth periods a rose can benefit from twice this amount.
But roses do not like wet feet, so don't plant them in standing water or in boggy areas.
6) Use local micro-climate to advantage. In very hot, sunny places such as US zone 8 & 9 some roses will find the blistering heat of summer overwhelming. Rugosas and Albas, for instance will often fare better if given a few hours of shade in the mid afternoon. This means that they can be placed on the east side of trees, fences, and houses so that at about two or three o'clock they get shade.
Similarly, one can often grow climbing roses a hardiness zone beyond their hardiness rating by growing them against a warm south wall. Zone 6 gardeners might dare to try Don Juan or even Lady Hillingdon against a south wall.
7) Beware of hungry trees. Many trees and shrubs send out strong lateral roots extending far beyond their drip line. These roots effectively gobble up water and nutrients. If you encounter roots as you dig the rose's hole you can be sure that the roots will negatively affect the performance of the rose. If the rose is vigorous and non-remontant the affect may be minimal. But if you are trying to grow a marginal cultivar on poor soil, the tree can make the difference between success and failure.
I have killed more roses by siting them badly than I care to admit. My biggest siting problem is my desire to grow roses in the shade. I have pushed the envelope in every direction: planting roses susceptible to diseases where they are a problem, planting roses outside their hardiness range, and planting roses where they cannot establishe without careful watering.
One fine spring afternoon I planted five Floribundas in an arc of sunlight that lay between two shadowy spaces. The path of the sun during the day lit most of the arc at least three hours. I finished the job feeling clever to have found a spot in a woodland to grow roses. But they all died. Some took two seasons to do so, but they died nonetheless. As the sun moved north during the summer, the illuminated arc moved south. By June the roses had no direct sun at all.
In another case, I read that the rose 'The Fairy' could withstand shade. So I planted it under some dense trees. I then forgot to water it in, or else never watered it again. The rose never got started.
One time I decided to plant six 'Old Blush' in an arc. I dug the first one into a nice hole two feet across and eighteen inches deep. In digging the next one in I encountered a limestone slab. I used a digging iron to excavate some of the slab, then planted the rose in a nice big hole. The dirt over the third site was thinner and I was a bit more tired, so the rose was planted a little closer to the limestone. And so it went until all six roses had been put into the ground.
A year later, the first rose I planted was four feet in each direction and was in flawless health. The next one was a little smaller. Each rose was smaller than the ones planted before until finally the last rose was about 2 ft high and showed signs of chlorosis.
The main issues in siting roses are: sunlight, soil, water, root competition, and temperature. If these issues are addressed satisfactorily, any vigorous cultivar will thrive.
1) Choose a site with at least six hours of direct, unfiltered sunlight each day. If planting south of an overhang in spring, be sure that the sun doesn't move too far north to cast a shadow all day long on the plant at the height of the growing season in June. If planting north of a tree or building, be sure that the sun shines directly on it even during the low angle sunlit days of September. Note that some cultivars require a full eight or more hours of sunlight or a warm wall behind them to grow well.
2) If the rose is said to be 'shade tolerant' that means that four to six hours of direct, unfiltered sunlight should do. Some roses will survive on less, but few with thrive and bloom well. Unless you are willing to treat it as an experiment in pushing the envelope, do not plant a rose were it gets less than four hours of direct sunlight.
I once grew Madame Plantier on the north side of a house where the rose got zero hours of sunlight per day. The rose did survive for two years but it grew leggy and it never bloomed.
3) Use fertile, neutral soil. Roses thrive on neutral or slightly acid soil. My experience suggests that soil that is too acidic will make them more prone to fungal diseases; soil too alkaline will cause chlorosis. Soils that are extremely peaty or sandy may not be dense enough for many roses. Very heavy clay soils will need plenty of organic material and some sand mixed in. My own experience suggests that roses like fairly heavy soil with a good mix of clay, sand, and silt as well as lots of organic material. Roses appear to be more tolerant of clay than many favorite garden plants. And this is one reason I grow them.