Another way not as compact but a little easier to read/follow. Would also handle if uscfollow wasn't 1 or 0 Tho i don't know when/if that would ever happen.
 
	 
 
;; Toggle UCSFOLLOW using COND
(defun c:foo (/ v)
  (setq v (getvar "UCSFOLLOW"))
  (cond
    ((= v 1) ;; If it's currently ON turn it OFF
     (setvar 'UCSFOLLOW 0)
     (princ "\nUCSFOLLOW Desactivado")
    )
    ((= v 0) ;; If it's currently OFF turn it ON
     (setvar "UCSFOLLOW" 1)
     (princ "\nUCSFOLLOW Activado")
    )
    (T ;; If it’s some unexpected value, default to OFF
     (setvar "UCSFOLLOW" 0)
     (princ "\nUCSFOLLOW Desactivado")
    )
  )
  (princ)
)