Celina should use a thesaurus to look for synonyms to replace the words she has overused. Mike should use a grammar book to study the proper usage of the vocabulary he used. Toni should use a dictionary to look up the definitions of words to ensure she is using them in the correct context. All three should use proofreading tools to check for grammar errors.

Using a thesaurus can be helpful for Celina to find alternative words to diversify her vocabulary. This will prevent her from repeatedly using certain words and make her writing more engaging.

Mike, on the other hand, should consult a grammar book to understand the correct usage of vocabulary. This will allow him to improve his grammar and use words appropriately.

Toni should make use of a dictionary to confirm that she is using words in the correct context. Looking up definitions will ensure she understands the meaning of words and uses them accurately.

All three individuals should also utilize proofreading tools to identify any grammar errors in their writing. This will help them correct mistakes and produce error-free content.