Determine your risk capital, i.e., the total amount of money you're willing to risk in your trading. This should be money that you can afford to lose without it affecting your lifestyle. Calculate 1% of your risk capital. This is the maximum amount you're allowed to risk on any single trade.
For day traders and swing traders, the 1% risk rule means you use as much capital as required to initiate a trade, but your stop loss placement protects you from losing more than 1% of your account if the trade goes against you.