Hibiscus love the sun and need moist, well-drained soil. Keeping these plants watered will result in larger flowers and lush foliage. Deadheading will improve the appearance of the plant, but is not necessary for continued bloom. It is best to plant Hibiscus in the garden before the heat of the summer arrives, and should be heavily mulched the first winter. In spring, cut back any remaining stems to 4-6 inches tall before new growth appears. Do not trim back in fall. A strong pair of loppers or a saw will be necessary to cut this plant back. Be advised that Hibiscus is always one of the last perennials to emerge in spring. Be patient, even if you think it is dead, it most likely isn't. Its vigorous growth rate more than makes up for this late start, however. Japanese beetles find these plants especially delicious.
Perennial Hibiscus should be cut back to 4-6" from the ground in the spring. Since this plant doesn't leaf out until late, any time in spring before the new growth appears is fine. The stems are quite woody, so a saw or strong pair of loppers is necessary to cut through the thick stems.
If you want to get really bushy and full Hibiscus plants, when the shoots start to come out of the ground and are about 6-10 inches tall, pinch them in half. The pinch should be made just above a set of leaves, this will improve branching. Improved branching will yield more flowers. If you are really dedicated, you can pinch them back 2 or 3 times before the 4th of July. Each time you pinch, take no more than half of the stem and pinch just above a set of leaves.
You will get fuller plants doing multiple pinches. It is also perfectly acceptable not to pinch at all. The plant will have fewer branches, but it will perform perfectly well.