First of all, I’d like to say that I think many people get hung up on the structure of an essay or paper. Introduction, Body, Conclusion. My short answer to the first question is: you should start however and wherever you want. Of course, in your final draft, the “Introduction”should come first. But while you’re writing, if you feel more comfortable starting with the “meat”of your paper (body paragraphs), or, heck, even with the conclusion, that’s fine. In fact, depending on how you prefer to write, starting with the body may help you stay focused on your topic; likewise, starting with your conclusion might help give you a clear goal to work towards. In my opinion, it’s all up to your preference at that point.
For those searching for an idea about what to actually start typing on their first page, I have these remarks: try to be both interesting and logical. This means you will NOT begin your paper with a statement like, “This paper will…”and you will also not use something like a dictionary definition to try to grab your reader’s attention (it won’t). Now, I would also caution writers not to agonize over the perfect “hook”—if it doesn’t come to you initially, you can always add it later. Additionally, it does well to keep in mind that, while the introduction does provide background information, you still want to keep it all relevant to your topic (beware sidetracks here).
If you feel you are struggling with digressions, don’t panic; they happen to us all. Just be aware of this as you revise/rewrite your paper, and don’t be afraid to be critical. As you read through each paragraph, ask yourself: why am I writing this paragraph? Evaluate the worth of each sentence; do they all tie-in to help support your thesis/claim? Can you easily identify a strong topic sentence in each paragraph? By asking yourself these questions as you read (and write), you can prevent yourself from accidentally transforming your paper into something it was never meant to be.