At a fundamental level, it’s really simple. Your topic sentence, or first sentence of every body paragraph, should serve three basic roles:
- Explain concisely and clearly everything that happens in the paragraph that follows. On some level it is an introduction to the body paragraph after all. It lets the reader know what’s coming up and how it fits in to the rest of the essay.
- Connect clearly and directly to the Thesis Statement. It should be crystal clear how it supports the main argument in the essay, not obliquely and indirectly, but precisely.
- Transition from the previous thinking. You can transition from what you’ve just said in the last sentence in the previous paragraph or the content of the whole paragraph, but you don’t want to disrupt flow because you’ll lose the reader in a hurry.
At the end of the day, it’s about reader-based-writing rather that writer-based-writing. I always say to think about your reader as a lazy, distractible five year-old child. They don’t particularly care what you have to say or particularly care to listen. You have to give them the Gerbers version if you expect them to actually stay with you. Happy writing!