CLISP has an integration with GNU Readline.

For improvements for other implementations see: How to customize the SBCL REPL.

Most Common Lisp implementations will try to load an init file on startup:

Implementation	Init file	Site/System Init file
ABCL	$HOME/.abclrc
Allegro CL	$HOME/.clinit.cl
ECL	$HOME/.eclrc
Clasp	$HOME/.clasprc
CLISP	$HOME/.clisprc.lisp
Clozure CL	home:ccl-init.lisp or home:ccl-init.fasl or home:.ccl-init.lisp
CMUCL	$HOME/.cmucl-init.lisp
LispWorks	$HOME/.lispworks
MKCL	$HOME/.mkclrc
SBCL	$HOME/.sbclrc	$SBCL_HOME/sbclrc or /etc/sbclrc
SCL	$HOME/.scl-init.lisp

Sample Initialization files:

Implementation	Sample Init file
LispWorks	Library/lib/7-0-0-0/config/a-dot-lispworks.lisp

Common Lisp has a way to influence the compilation strategies. It makes sense to define your preferred values.

Optimization values are between 0 (unimportant) and 3 (extremely important). 1 is the neutral value.

It's useful to always use safe code (safety = 3) with all runtime checks enabled.

Note that the interpretation of values is implementation specific. Most Common Lisp implementations make some use of these values.

Setting	Explanation	useful default value	useful delivery value
compilation-speed	speed of the compilation process	2	0
debug	ease of debugging	2	1 or 0
safety	run-time error checking	3	2
space	both code size and run-time space	2	2
speed	speed of the object code	2	3

An optimize declaration for use with declaim, declare and proclaim:

(optimize (compilation-speed 2)
          (debug 2)
          (safety 3)
          (space 2)
          (speed 2))

Note that you can also apply special optimization settings to portions of the code in a function using the macro LOCALLY.