Where you're actually keeping the data (server-side data against a session, posted form paramters etc... ) would determine the method. Here's a simple example with posted data. Firstname is sticky after the form is submitted, surname isn't.

#!/usr/bin/perl
use CGI;
use CGI::Carp qw(fatalsToBrowser);
use warnings;
use strict;

my $q = new CGI;

my $firstname = $q->param('firstname');

print qq|content-type: text/html\n\n|;

print qq|<form action="$ENV{SCRIPT_NAME}" method="post" name=f>\n|;
print qq|<input name="firstname" type="text" value="$firstname"/><hr/>
+|;
print qq|<input name="surname"   type="text"/><hr/>|;
print qq|<input type="submit" name="form_submit" value="go">|;
[download]