Regardless of the type of essay you're writing, a strong introduction is crucial for success. The introduction bears the responsibility of both hooking the reader and communicating the thesis. Several ways exist to accomplish both goals; however, the mode of essay will determine which techniques are appropriate and most effective. In a narrative essay, a statement of statistical analysis is probably not right for the task. Conversely, a narrative anecdote isn't appropriate for a lab report.
Hook the Reader
The hook, in the simplest terms, is the opening sentence or two of an essay and is responsible for grabbing the reader's attention and generating interest. A strong hook could be an interesting fact that communicates the urgency of your thesis. It could be a generalization that serves as a foil for your argument. Anecdotes are also useful for introducing the reader to a topic while also establishing your attitude toward the subject. Whichever technique you choose, make sure it's interesting and serves your thesis.
From Hook to Thesis
Your hook is the opening of the introduction, and your thesis statement is the end, and so you have to write from one to the other in a way that makes sense and places emphasis on your thesis. This means that if your hook is a startling fact about the costs of healthcare, and your thesis is a plan that will solve the problem, you should work toward your thesis by explaining why your thesis is fresh, necessary and timely.
State (or Imply) Your Thesis Clearly
The decision whether to state or imply your thesis is a tricky one. To imply your thesis means you must be sure your entire argument is so clear that every reader will interpret your thesis in the exact same way. When using this style, your hook will often be a narrative anecdote, one that communicates a problem so effectively that the idea doesn't need to be expressed directly. However, if you are using a thesis statement, make it the final sentence of the introduction, and word it with surgical precision.
Transition Toward an Interesting First Topic
If you used a thesis statement at the end of your introduction, then you don't transition into your next paragraph; you simply begin the next paragraph with a strong topic sentence that follows logically from the introduction. However, if you are implying your thesis, you need to transition out of your introduction in a way that flows smoothly and is logical. For example, if you have been writing about problems with the public education system, you should mention in your final introductory sentence the specific educational issue you will discuss in the following paragraph, and why it is important.