We have a lovely callistemon at our bowling green. No pruning is required, only to maintain a good shape. You can cut off side shoots if not required. Best to remove any dead shoots anytime or damaged ones early summer late spring.

Not a good time to take a lot off now, too late in the year - usual procedure is to cut back immediately after the flowers are finished, trimming just beneath the spent flowers - you can also reshape at the same time if necessary.