Extra whitespace to put the `cond` clauses in columns can make it even more clear, for "visual" looking at code, rather than only "verbal":

    (define (member? item set)
      (cond ((null? set)             #f)
            ((equal? item (car set)) #t)
            (else                    (member? item (cdr set)))))

For bonus points, line up the key variable in the clauses, and it's easier to see visually that the `cond` is about that one variable:

    (define (member? item set)
      (cond ((null?       set)       #f)
            ((equal? (car set) item) #t)
            (else                    (member? item (cdr set)))))

Which accidentally also lines up with one of the procedure's arguments, though I didn't intend that one, but you could double down on that:

    (define (member? item      set)
      (cond ((null?            set)  #f)
            ((equal? item (car set)) #t)
            (else                    (member? item (cdr set)))))

This isn't some deep thing; just a little example of how sometimes whitespace, other than just indenting at the beginning of the line, helps to exposure some of the structure visually.