A jack plane is used to remove a lot of wood quickly. To do this, you need to sharpen your blade with a curve in it, which allows you to set the blade quite deep but still allows you to be able to push the blade through the wood without undue hardship.

Starting with a square blade, that has been preferably hollow ground, use a 1000 grit stone to hone the bevel on the left hand side of the blade. See photo. 
To form a slight curve on one side of the blade, you will need to keep moving the pressure point that the blade contacts the stone. Starting on the outer edge of the blade and move toward the centre, thus making a uniform curve. Then repeat on the right hand  side of the blade to form a complete even curved edge across the width of the blade.

NOTE: Picture not to scale.  Also you could take the 0.5mm out to 1mm if you want to take deeper but narrower cuts to suit a particular task.

Once you have a nice curve on the blade (close to the dimensions shown on the adjacent diagram), you can go ahead and refine the edge using finer grit stones. I use a 1000 grit  stone first,  then a 6000 grit stone to finish off with.   The back of the blade is honed perfectly flat in the same way you sharpen any blade.

 When you are honing the curve on the blade be careful not to dig the blade into the stone, particularly your 6000 grit finishing stone, as it is easy to do. A light honing pressure will help with this.