I’m still not sure where to begin. If you are still stuck for a first sentence, look at the keywords you are considering. If similar recent papers in your target journal begin with a definition of or a fact about one of those keywords, consider starting with that; if they begin by establishing the importance of the topic, begin with that. Remember the key message: Evidence-based guidance can be obtained by studying the structure and language of successfully published papers. Can’t I start by describing the specific problem I am hoping to solve? Most authors don’t, because it’s sometimes difficult to describe the specific problem until readers have enough information to understand it. It’s also very hard to limit yourself to one sentence about the problem you are hoping to solve, and before you know it, you’ve written a lot of specific detail about the problem, which your readers can’t process because you haven’t yet given them the relevant background.