The overhead cast can be improved on by using a method called the "unitech".
To begin, place the sinker near your feet in the "start" position as shown in the photo.

Don't be tempted to step forward as that would defeat the advantage of centrifugal force which you need to attain distance.

Be sure you maintain enough tension on the line to make sure the rig stays clipped if you're using a clip down rig but not enough to lift the sinker
(if you're not using a clip you should be, it keeps the bait from doing an imitation of a helicopter).

Keep your leading arm higher than the trailing arm.

What happens using this method is that when you start the cast, the sinker will lift off the ground and swing away from the direction of the cast.

This begins the "load" on the rod which in turn helps you generate the stored energy needed for a long distance cast. As the cast progresses, you are pulling down and into your body with the leading hand as you "punch" up with the trailing hand.

The leading and trailing hands become lower and upper as the rod is leveraged through the cast. It is important to continue pulling the lower hand into the body at the same time you are pushing with the upper hand. Practice will tell you the best release point for distance and accuracy.

This is a very safe cast and it will increase the distance you get over the standard overhead cast.