Risk per trade
Risk a fixed small % of your account per trade — 1-2% max. Position size = (account × risk%) ÷ (stop distance in pips × pip value). Never size by "how confident I feel."
Worked example
$1,000 account, 1% risk = $10 risk. Stop = 20 pips. On a pair where 1 lot = $10/pip, 20 pips = $200/lot, so size = $10 ÷ $200 = 0.05 lots. ShaFX calculators do this for you.
Common failure
Fixed lot size regardless of stop distance → inconsistent risk → eventual blow-up.