A. Global economies suffered. Tariffs were high. Unequal distribution of wealth - caused people to not have money or jobs to buy items needed to keep the economy going. Length and severity of Great Depression went far beyond the normal rhythms of the business cycle. Availability of easy credit. Buying on speculation - buying and selling quickly for profit; caused prices to be "inflated". Investors used margin buying - purchasing stocks with borrowed money.
B. Use money that you already have to buy stock and don't just buy stock to make a quick dollar.