Heya @AymanFathy
I personally would suggest to look over EX294's list of objectives, and prepare for each individual objective.
As you've passed RHCSA, you know the format of the exam. RHCE is going to be similar in terms of the exam structure.
Just like RHCSA, it's also performance based, so you should have practical experience with each and every one of the objectives. I'd suggest using Vagrant to provision several VMs, and dive into each of the topics.
Note that the exam lasts 4 hours, so I personally wouldn't skip any of the objectives. 4 hours is a lot of time ;).
