"The" is the only definite article we have in the English language and there isn't an actual substitute for saying "the lawn," "the dog" or "the man." We use "the" when there is only one possible thing it could be talking about, and the audience knows exactly which one it would be.
In general, you really can't overuse the word "the." However, your question is probably referring to the problem of your sentences sounding too simple and general. To get rid of that problem, you can substitute a clearer and more specific description of the thing you are referring to rather than the simple "the ...." Here are some samples:
"The man" could be John (his name), our dentist (our relationship to him), that man I met in the subway (a description of a situation), that rather thin and older man (a description of his appearance).