Move to the beginning of the document:

gg

Move to the end of the document:

G

Move to the top of the screen:

H

Move to the bottom of the screen:

B

Move to the middle of the screen:

M

Move one full screen forwards:

<ctrl> f

Move one full screen backwards:

<ctrl> b

Move one half screen forwards:

<ctrl> d

Move on half screen backwards:

<ctrl> u

Move to the beginning of the current line:

0

Move to the end of the current line: