A useful way of tackling this question would be to split your ideas of the possible factors into those based on structural phenomena and those driven by the agency of individuals. In this way, your answer would consider both long term trends and factors, such as the inherent weakness of the Weimar Constitution and the impact of the economic crisis from 1928 onward, as well as assessing the role and influence of key actors, such as Hindenberg, Schleicher, von Papen and Hitler. A strong answer could also consider how these structural and agency-based causes influence and relate to one another. For example, when assessing the weaknesses of the Weimar constitution it should be noted that these weaknesses were only relevant if exploited by an individual. Also, the successes of individuals working to bring down the democratic system, such as Hitler were only possible due to structural context such as the economic crisis.