Programming style
These are suggestions for programming style, some undisputable, some my (Stanisław Halik) whims.

  • Always put parenthesis after the previous expression on its line, never on a line by itself. If you have trouble reading code formatted in this way, ignore the parens (or make them disappear by regexp-replace or font lock) and look at indentation.
  • Use long, descriptive variable names. It's +buffer-size+, not +BUFSIZ+ or similar. This immensely helps reading comprehension and generally alleviates the need to comment the code (see below). I can't bring myself to read uncommented code in languages that don't allow hyphens in variable names, while I can read people's Lisp just fine. It doesn't apply when abbreviations are widely known (e.g.retval, i). Also abbreviate extremely long symbol names, e.g. frobnicate-svuc might be preferred to frobnicate-slot-value-using-class if the code is expected to fit in 80 columns.
  • Comment non-obvious stuff. For instance, once I wrote the following code:

    (defmacro fn (&environment env &body body)
      (with-walker-configuration (:undefined-reference-handler nil)
        ;; .VARS is modified implicitly in macroexpansion of the form
        ;; package protects against leaking symbols
        (let* ((.vars nil)
               (macro-name (gensym))
               (ret (macroexpand-all `(macrolet ((,macro-name ()
                                                   (car (push (gensym) .vars))))
                                        (symbol-macrolet ((_ (,macro-name)))
                                          (progn . ,body)))
          (declare (special .vars))
          `(lambda ,(reverse .vars)

    and had to add the comment because it wasn't immediately obvious what this code does.

  • Instead of (if some-list .. ...) use (if (not (endp some-list)) ... ...). Instead of (if (lookup foo) ... ...) use (if (not (null (lookup foo))) ... ...). Basically, only use a bare expression in conditionals if it uses the -p convention.

Other Style Guides

document macro example