This procedure depends on the distribution you are using. For Debian/m68k 2.1 (slink), you will need at least the following packages (get the latest versions available):
xfonts-base
xfree86-common
xlib6g
xserver-common
xserver-fbdev
For a fully functioning X installation, you'll probably want a decent window manager (fvwm2, fvwm95, AfterStep, WindowMaker, icewm...), some more X packages (like xcontrib) and some more fonts.