mgrindy, the gurus say you shouldn't risk more than 2% of your capital ON ANY ONE TRADE; in your case this would be $40. You'll lose that in brokerage alone on one trade with Commsec and many, many stocks will swing all that and more in one day.
I'm more of a long-termer, using weekly charts, so I have a stop loss set at 15% of the buy price or 1% below the most recent turning point at the bottom of a downtrend, whichever is the lesser of the two.
The main thing is having a plan, setting a stop loss and then adhering to it and pulling the trigger to sell when you're at the point that you know you're wrong. This way you'll preserve your capital and live to trade/invest another day.
