Reading another topic I get the feeling that this little, but important, trick is not well know.
To play Quake most probably you want this little autoexec.cfg file in your quake directory.

The idea is to allow always run in all direction (including strafing), activate mouse look, disabling auto aim, and finally make the "run" key a "walk" key.

For some reason the "Always run" in the menu actually increases only the forward speed and not the strafing speed (+speed increases all speeds instead), the auto aim is usually more a chore than helpful overall with rockets, and walking instead of running might be useful if you need precise movement, but it is an exception more than the rule so the key is for walking instead of running.

Of course, you can use another key instead of shift.

autoexec.cfg
-------------
+speed
+mlook
sv_aim 1

alias +walk -speed;
alias -walk +speed;
bind shift +walk;