First and most important is to make sure the stem is securely staked, and that you don't plant it in a very windy position. Second, feed in about April with a specialist rose food such as Toprose, and repeat 6 weeks later. Third, have a fungicide spray and a spray which treats for aphids handy for use from early April through till end September - systemic is best. The fungicide is to prevent/treat black spot, and the aphid one is for aphid infestation (obviously). Systemic will mean you only have to spray fortnightly. Fourthly, deadhead by cutting off the flowered stem about 6 inches down, or to the nearest outward facing, proper leaf, angling the cut downwards from the leaf/stem junction.
Prune in Spring, removing dead, diseased and any crossing growth, and reshape as necessary, always to an outward facing leaf/bud. Do not, though, cut lower than the graft point at the top of the standard stem.