There are a number of commercial push sticks and push block available, but it is just as easy to make one. There is not just one ideal shape or size. This varies from woodworker to woodworker, machine to machine, and application to application. There are three basic designs that you can customize to meet your needs. Make your push sticks and blocks from straight, clean, hardwood.
Plywood is preferable since it is less likely to split, warp, or crack.
Round the handles to prevent splinters. The push stick is useful for feeding narrow stock between a featherboard and a fence. It is usually designed at a 45degree angle with a small notch at the end. The push stick allows you to apply a great deal of downward and forward pressure. The rectangular push stick is used to apply greater downward pressure on wider stock.