How would I go about answering the question "What was the primary motive of the people who went on the First Crusade?"

The first step in answering such a question is to clearly outline your thesis in the introduction. The introduction should be clear and concise, and show immediate engagement with the question. Try to avoid lengthy intros giving lots of descriptive background knowledge. The introduction should also give your essay a structure which the reader can easily follow, you should follow this structure throughout the essay. For the main body of the essay you should consider the different factors which possibly served as motivation for the people who went on the First Crusade. You should consider one factor per paragraph and you should carefully think about the order in which you discuss them. You may choose to write about the strongest factor first and then the weakest last or do the opposite and have a "crescendo" effect in your essay. It can be effective the end the essay considering the strongest factor. After you have completed the main body of your essay and explained which factor is the most important and why you should finish with a strong conclusion. This should tie in with the thesis outlined in your introduction and should show clear argument as to why you think said factor is the most significant. The conclusion should contain no new material.

For an essay such as this the key factors which you should be considering would be genuine piety, worldly gain, feudal obligation, tradition and papal ambition. The key historians theses which you should consider including in such an essay would be Riley-Smith, Phillips, Asbridge, and Frankopan. The general modern interpretation by said historians is that the primary motive was in fact genuine piety. Therefore if this is the line of argument you choose to take then state that you are agreeing with one or more of these historians and say why. A good observation to make is that they corroborate and pointing this out will strengthen your argument.