If you have not installed your WordPress yet, it is a good idea to change the default database prefix before making the installation. You can easily do this by modifying the following line in the wp-config-sample.php file;
$table_prefix = 'wp_';
Change it to something more complex, for example:
$table_prefix = '1w27p_';
Once you make this change, rename wp-config-sample.php to wp-config.php and proceed with the WordPress installation.
This can be done also by using the WordPress installation web interface. You should simply enter the desired database prefix in the Table Prefix field of the web installer interface.