When we are "concentrating on" something, we are giving it our full attention and focusing solely on it. However, there are many synonyms that can be used to convey the same idea. Some examples include "centering on," "fixating on," "immersing oneself in," "zeroing in on," "directing one's attention to," "dedicating oneself to," "engaging in," "devoting oneself to," "delving into," "focusing intently on," and "paying exclusive attention to." Each of these phrases can be used in place of "concentrating on" to provide variety and enrich your writing's vocabulary.