Quote from macintash:
The question is not if a good trade exists. The question is, if/when there is one how much would you risk. That's it
And again, there is no such thing as a "good" trade. In fact, some of my best trades looked extremely bad right from the start.
That said, a trader should never risk more than 2 to 5% of his capital on any given trade, no matter how "good" it appears to be.
Trading is a marathon, not a sprint.