In order to trade in a falling market, you need to have certain knowledge and experience. If you are not well versed in the issue, then it is better not to do it. It is worth considering that margin trading can bring you big losses.
Margin trade is like gambling and the less your percentage of risk the better for you. I have been involved in this margin trade when i was trading forex and you have to focus much on how to reduce risk if you desire to stay long in this market.