This comes from personal thoughts and If you've been through the RHCE exam, please add any tips you found useful!
- Start with the RHCE Exam Prep Guide from Red Hat. Seek to ensure that you are comfortable with every topic there.
- Create a practice environment with at least 2 networked machines (four would be better) and begin practicing. Virtual Machines in VMware will suffice for this if you have access to a VMware server. Create one or more of these systems to be an untrusted "cracker" system. Configure each service mentioned in the Exam Prep Guide. Test it. Secure it so that it cannot be accessed by the untrusted system.
- AFTER you are comfortable with the topics in the prep guide, if possible, enroll in the RH300 course from RedHat. DO NOT rely on the course alone -- prepare heavily before attending the training. It will fill in many gaps, but moves VERY quickly and will swamp you if you don't already understand the basics.
- Get comfortable with working at the command line and with vi as your text editor. You'll need to be able to function quickly and without hesitation in situations where you might not be able to launch a graphical interface.
- Learn how to start system configuration before an installation even completes (and practice this). As soon as the installer begins installing packages, you can use Ctrl-Alt-F2 to get a virtual terminal. If you then chroot /mnt/sysimage you can start creating users and groups while the install is still going on.
- Partner with others who are also preparing for the exam. Form a study group. Divide up the topics you need to work on and teach the others the topics you've studied (you learn a LOT from preparing to teach others).