The biggest challenge on this exam will be ur ability to manage ur time. This is even more important now because exams r given on virtual machines most probably. Also the actual test instructions will be on the screen. This means u will be flipped thru different windows very often, which can be a huge time waster if u are not careful.
U must be very comfortable with RHEL 6 KVM setup & must know how to use a KVM virtual.
U must know how to restrict access to machines and servers. Iptables can do job of this but please don’t forget about tcp_wrappers and the /etc/hosts.deny & /etc/hosts.allow config files. Most of that kind of exam is about network services.
Of-course know how to setup/configure iscsi.
Never disable FIREWALL.
And last but not least, Make practice and practice especially on command line tools and scripts. Read their study mats, search on the web for RHCE or gather info from other sources.
See here for more:http://blog.tuxforge.com/rhcsarhce-study-guide/
and also link here: www.azhowto.com/2009/01/25/rhce-tips-my-experience-part-2-taking-the-course-and-exam/

tips that are not covered by the NDA
read the redhat documentation and learn to work on rhel OS's