The first thing you need to do is source as many free images of hands as you can find.
Once you have built a file of images you can use these as
references to help you draw your hand. What I did was use them
images to
create a page with as many different poses as I could fit onto it. I used
MS paint to do this and then printed it off so that I had the images
in front of me for reference before I began.
I studied the pictures I had gathered for some time trying to
dissect them into sections that I could sketch to form the basic
shape of the palm, thumb and fingers. I try to view all things in
terms of circles, squares, ovals or rectangles as it helps me form
the shapes of the images I wish to portray.
I started with a basic picture of the hand viewed flat from
above.

The first thing to do is draw an oval and a rectangle overlapping
each other making sure that the narrower end of the oval is at the
point of the wrist.

Find the centre of the rectangle where it crosses the oval and
lightly make a mark. Using this point as the middle of the index
finger start to divide the rectangle into five equal parts. These
will give you a rough guide to the location of the fingers and
thumb.

Next I decided the furthest most point for the tip of the index
finger in proportion to the rest of my hand and marked it on the
index finger (no3)
and then divided the distance between my mark and the top of my oval
into three sections making sure my top section was slightly less
than the other two which I spaced roughly equally apart. This will
give me my points for the joints. Once I had done this I then
decided the point of the tip of the little finger and marked it on
the edge of my rectangle. I have found that this point is roughly
inline with the centre of the middle section of the other
joints of the finger.

The next thing to do is to draw almost a 90 degree angle from the
tip of the little finger passing through the tip of the index finger
and down to roughly the same point on the the edge of the fourth
finger on the opposite side of the hand.

Once you have done this all you will need to do is to add all the
points where the joints of the other fingers will be in relation to
each other. To do this I roughly copied the arc of my first 90
degree angle making sure it passed threw the points that I had
already marked on the index finger (no3).

Now you have a rough idea of where everything is in proportion to
the rest of the hand you can start to fill in the fingers and the
thumb.
Starting with the index finger (no3) begin to fill in
between your reference points as you shape each individual digit. I
treat each section as a sausage and join the together between the
marks.

Once you have done this remove all of the guide lines and begin to
properly shape your hand paying particular attention to the finger
nails knuckles and thumb in relation to how it meets the rest of the
hand. You can use your initial outline for the front of the
hand also, as shown in illustration. To spread the fingers use the
same method as before only draw each digit separately in the
desired position.