How much to risk?

How much of my capital should I risk and why? I hear some do 3-5% others do 10-20. Any pointers?

You have to set your own rule based on the expectancy of your system. A good rule of thumb is 2 - 3%.

Size your position so that if the trade hits your stop you will lose no more than 2 - 3% of your account.

I risk 5% per trade.