I avoid putting (server-start) in my config as I like to start stand-alone Emacs instances too.
So I use emacs --daemon instead.

Similarly, I'd like to retain an Emacs config that works on WM other than EXWM, so I don't put (exwm-enable) in my config either.
(Note: calling exwm-enable from within another WM seems to have no effect. To be confirmed.)

If you are in the same situation as me, you'd be tempted to add this to your .xinitrc:

exec emacsclient -a "" -c --eval "(exwm-enable)"

or

emacs --daemon
exec emacsclient -c --eval "(exwm-enable)"

To your utter dismay, it won't work. This, I believe, because the Emacs frame (-c) must be spawned after exwm-enable was called.

The solution is very straightforward:

emacs --daemon -f exwm-enable
exec emacsclient -c

I think it might be worse documenting this in the wiki. Any comment?