1. Make sure you have enough funds to open and maintain trades and don't open more positions than you canmanage with your account equity.
2. Manage your risk. Keep an eye on your Usable and Used Margin.
3. Don't invest more than 2% of your account balance. Place stops to protect your equity from significant losses.
As Paul Tudor Jones (a great trader, by the way) put it: "I'm always thinking about losing money as opposed to making money. Don't focus on making money, focus on protecting what you have"