If you have at least the basic Photoshop knowledge, making caricature shouldn't be too hard.
I'm going to show you, the easiest way to make it.
I'm going to use this Madonna photo for this project.

Step1:

First thing we have to do is to open some picture(picture 1)

Picture 1

Step 2:
This step is optional and you can skip it (go to the step 5, if you don't wan't to move the background), but It looks better, if you move the background first. The easiest way of doing it is to double click the layer, so we change it from a background layer to layer 0 (pictures 2 and 3).

Picture 2

Picture 3

Step 3:
Make a new layer (layer 1) and fill it with white. Than drag it to the bottom of your layers window (picture 4 and 5).

Picture 4	Picture 5

Step 4:
Now we are going to use the eraser tool and erase a background around Madonna, so we well get some nice white background.(picture 6).

Picture 6

Step 5:
Now the real party starts. Use the liquify filter (shift+ctrl+x). First select the Bloat tool (picture 7) and make a nose and the eyes a little bigger, you can make the whole head bigger (pictures 8, 9,10,11).

Picture 7	Picture 8

Picture 9	Picture 10

Picture 11

Step 6:
Now we are going to use the Forward warp tool (picture 12) and drag the chin down, drag the mouth down, squeeze the face etc(pictures 13 and 14).
For the and we can add some colours(ctrl+u)(picture 15).
We can add some effects and use some brushes to colour our caricature a little beat and that's all.

Here is our final result!