Enable Mouse Look

+mlook
v_centermove 10
sv_aim 1

where:

+mlook enables mouse look,
v_centermove 10 stops centering the screen on mouse move forward and backward,
sv_aim 1 disables auto-aim.

Execute Commands on Startup

A file can be created at ID1/autoexec.cfg containing commands line-by-line to be executed whenever Quake starts.