In some of my manga sketches i got troubles in making the hands. For me the hand is more complicated than the other parts of my manga sketches characters. But with the help of some tutorials i had to know how to do a simple but a perfect hand. For example on this image, there are circles, lines and polygon show. The circle serves as the joints of the hand. From the palm to its fingers. and the lines serves as the fingers and the polygon is the palm. If you done placing all the elements you can now add some more details o complete its real shape and form.
There are other manga sketches uses simple shapes. Like on this image, it shows the artist uses ovals and circles to create his hands. And he just added some more details to create his simple cartoon hand.