In many ways each paragraph is an essay in miniature. The paragraph h as a topic sentence that states the main idea of the paragraph in the same way a thesis statement presents the main argument of an essay. A paragraph is a unified, coherent set of sentences.
All sentences relate to the main idea in a well-developed, supportive and consistent manner.
It is essential that all ideas and entences flow logically and smoothly throughout the paragraph. The topic sentence presents the main idea. The topic sentence is written in a way so that there's a smooth transition of ideas between what was stated in the previous paragraph and in the new paragraph. Present the paragraph's key argument clearly and substantiate it with quotations and sometimes, with data. Avoid ending a paragraph with a quotation.