I would avoid margin trading unless you're a real expert. It's high stakes, and you can lose a lot of money very quickly. If you really want to do it, then I'd recommend building up a lot of experience in normal trading first.
One big rule of trading is pick a site and a coin that has high volumes. If you try to trade somewhere that has a big spread between the top buy order and the bottom sell order, then you are putting yourself at a disadvantage from the start.