It depends on what capital you are trading and normally to my money management rules i trade 1 lot for every $1000 in my account and if i have $3000 then I will trade 3 lots i.e for every lot you trade you should have 1000 pips in your account to protect the margin and a stoploss of 25 pips thus when you trade you will risk only 2.5% in your every trade...