Before you can begin to determine what to write in a paragraph, you must first decide on a main idea or thesis statement for your paper. What is the most important idea that you are trying to convey to your reader? This is true for any topic. Here is an easy formula to remember.
Topic/main idea + your opinion = Thesis (usually stated in Topic Sentence)
Thesis example: Vigorous and very physical play is important to children's development and learning.
Topic/Main idea: Vigorous and very physical play + Opinion (controlling idea): is essential to children’s development and learning.