Positioning
Echinacea purpurea is a native of prairies and open woods and therefore will do best in full sun or partial shade. Too much shade will result in significantly fewer flowers, and weaker stems, which isn't what you want for E. 'Razzmatazz's heavy flowers!

Soil
A well-drained fertile soil is favoured. This can be neutral to alkaline. Echinacea purpurea has very good drought tolerance, but it is important to keep the soil moist after planting until the plants are established.

A good amount of organic fertilizer applied in spring will encourage better growth and development. In poor soils an extra amount in summer might help to prolong flowering. If you are not using liquid fertilizer, make sure that it gets washed in, so that the roots can absorb it. 

Continuous flowering
Deadheading will prolong the flowering period for normal E. purpurea, but as this fully double flowering mutant does not set seed, it will keep on flowering continuously.  The E. Razzmatazz in our display garden is surrounded by several other E. purpurea cultivars and did not produce seeds at all. On the other hand it will still look better in the garden if you remove the dead flowers.

Diseases
Echinacea purpurea has very little in the way of disease problems. Some leaf spots may occur, but these will not be lethal, and after dormancy the plant will emerge again with healthy leaves.

Links
Another website you might like to check for information on growing Echinacea is Perennial Flower Gardening.