Well hibiscus come in two groups: tropical and hardy. You don't say which one you have, but both can be pruned back if they are too leggy. This should encourage new growth. However, this leggy growth is probably a symptom of something else going on. If your plant is not getting enough light, it's likely to be growing like this. Hibiscus requires full sun (at least 6 to 8 hours a day and a rich, organic soil) to look its best.