Only risk what you can afford to lose
Trading and investing can lose money, including — with some products — more than the amount put in. A common principle is to decide in advance how much of a total account any single position may risk.
Common tools
Position sizing: choosing how large a position is, given how far price could move against it.
Stop-loss orders: instructions to close a position at a set price. They can limit losses but are not guaranteed to fill at that exact price in fast markets.
Diversification: spreading exposure so one outcome does not decide everything.
Leverage
Leverage magnifies both gains and losses. Leveraged products such as CFDs and margin trading are high-risk, and regulators in several regions require providers to disclose the share of retail accounts that lose money.