As mentioned previously you can use C-l to recentre the window on the line containing the cursor (point in emacs terminology). A related command is move-to-window-line-top-bottom which is bound to the short-cut M-r. Use this repeatedly to cycle the position of the cursor (point in emacs terminology) between the top, middle and bottom of the window.

In other words, C-l recentres the window while keeping the point on the same line, while M-r moves the point without recentring the window.