To compose clear and coherent sentences using past and present tense, ensure you maintain consistency in your verb tenses within each sentence and paragraph. For example, if you're describing something that happened in the past, use past tense verbs consistently throughout that description. Similarly, if you're discussing something that is currently happening or generally true, use present tense verbs. Avoid switching between past and present tense within the same sentence or paragraph, as this can confuse your reader.