A dozuki cuts only in one direction -- on the pull stroke. You can push the saw through your workpiece, but only apply pressure when pulling towards you.

Begin your cut by placing the bottom edge of the saw on the corner edge of the workpiece. Make sure the saw blade lines up with any markings you made on the workpiece for this cut.

Gently pull the saw down and towards you.

here is a new point

Repeat the above steps for a couple of more pulls, ensuring you take the saw out of the workpiece after each pull. This will allow you to start a neat and precise cut into your workpiece.