Answer: I am assuming you have a tropical hibiscus plant. There are two ways to prune these. One is to cut it back quite hard in the fall when you bring it indoors, or in the late winter before it begins to grow again for the season. Give it an overall cut back, removing about half the branch length and creating a symmetrical outline. The plant will take several months to recover, regrow and begin blooming again. This is not as big a loss as it might seem because often they do not bloom well while indoors for the winter anyway.
The other approach is to thin it a little at a time all year long, removing one or two of the longest branches at a time. This is preferred for plants that are grown outdoors year round or in a greenhouse or conservatory in winter because it will not cause a break in flowering.
I hope this helps.
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