Without intending to, we can fall into the habit of issuing commands to our readers, urging them to undertake complex logical computations with a single word. We've all seen the paragraphs, sections, and even abstracts that begin this way:
Reader thinks, "Suppose it yourself."
Reader thinks, "No thank you."
Reader thinks, "Why should I?"
Of course, I'm exaggerating to make a point.
But if you find that you are beginning by issuing orders to the reader, you may want to reconsider how you structure your writing. As an indicator, look out for imperatives, especially at the beginning of paragraphs or sections, and find ways to defer the order until you can offer an incentive for taking the action you want them to take.
Offer an incentive to follow the order
At some point, you probably will need to ask the reader to do something. In such cases, you can offer them an incentive. Here's the difference:
No incentive: Suppose x increases.
Some incentive: The key variables—x and y—are related through channel z. To see how, suppose x increases.
It may not be the perfect solution to a tricky problem, but it is kinder than beginning with an order.
So, does your paper have any "Horse: Jump!" writing?