After installing MySQL, the first thing you’ll want to do is reset the root password for MySQL. You can achieve this using the following command:
[root@myhost]# mysqladmin -u root password new-password
Set MySQL to start automatically with the following command
[root@myhost]# /sbin/chkconfig mysqld on
Update:
A much better way to secure your installation of MySQL is to run the mysql_secure_installation command. This prompts you to set or change the root password, remove guest access and test databases, etc.