There are several tips to help hit a softball farther. One of the easiest tips is to rotate your front foot towards the pitcher as you start to transfer your weight during the swing, this helps to open your hips more producing a increase in power. Another tip would be to try to hit the ball to the opposite field rather than pulling the ball, this will force you to wait on the ball and load up your swing more. Another way to increase power would be to use a slightly lighter bat, increasing bat speed. Try any or all of these to help achieve your goal of 400 feet.