Venezuela was a very rich nation in terms of per capita GDP and compared to most Latin American it was ahead. It also had a long tradition of democratic governments, unlike many of the other Latin American nations. The source of the wealth was primarily oil.
Venezuela reached its best levels of economic success in the 1970's, when oil prices were high. However, due to the following reasons, in the 1980's the economy started to decline and nowadays it reaches the levels of an economic disaster.
In the 1980's the price of oil abruptly declined causing a decrease in the cash inflow into the country. Venezuela, suddenly was in a situation in which it was difficult for it to pay for the large incurred debt of the 1970's. Venezuela did not diversify its economy. High oil prices brought some relief from 2003 till 2007, but when the price of oil collapsed again, the problems repeated.
Corruption has been rampant always. This problem does not only bring loss of resources, but also political instability. Investors do not like t invest were there is too much corruption.
US sanctions contributed to make things worse for Venezuela. The basis for this sanctions are the lack of respect for democratic institutions and certain associations of its leaders with drug trafficking
Socialist policies are not the best for wealth creation. This and the continuous clash of the government with the business class created a problem with investment. If there is no investment, there is no growth. Because of this, (and the lack of oil revenue) the government resolved to print excess money, resulting in hyperinflation.
Finally, the ideological nature of the government made it create associations with other poorer Latin American countries. Venezuela lost oil and resources supporting regimes such as Cuba's, without getting much in return.