Thesis statements don't have to be complicated. In fact, the simpler, the better! The best tip I can give is to focus on your main idea and make it clear in one or two sentences. When I write for my blog, I start with a broad topic and then narrow it down. For example, I wanted to write about investment strategies, so I kept asking myself what the main point was. I ended up with: "Diversifying your portfolio is key to minimizing risk in uncertain markets." This simple statement helped me stay focused while writing. A clear thesis makes it easier for your readers to understand what you're saying, and it keeps your writing on track.
As I discuss in my writing book, An MFA For Your MBA, specificity matters. This is especially so when creating a thesis statement, as it will help narrow down your topic and overall scope of your paper (or whatever it is your writing). As you would with any paragraph or sentence, you want to avoid ambiguity and keep yourself (and your reader) focused on what you're talking about-and only what you're talking about. A specific statement that is well-defined is easier to defend and leaves little room for misinterpretation. This goes for term papers as well as emails.