Or if all goes fine just use compounding.It really depends on the individual and his financial state. $100-$200 would be a good amount to start with and as the time passes, more investment could be made if there are chances of profits.
In my opinion one should start with less amount so If things may go wrong then one can afford to loose the small amount. I would like to deposit $30 to start my trade and then will slowly increase it according to the my trading strategy.