Am preparing RHCSA exam 200
am preparing based on exam objectives displayed in redhat site. By watching youtube tutorials and practicing in oracle virtual box.

is that right way to prepare or need to add any ?

Real-world practice (as you're doing with the virtual machine) is excellent. Watching videos may (or may NOT) be good, depending on whether or not the video is accurate, up to date, and shows everything.

Better question would be WHY you're getting a 'certification', and how long you've been working with Linux. Because getting a certificate before you have any experience/knowledge is fairly pointless, and it will be VERY obvious at any job you get with your 'certificate' that you don't have the experience to back that up. Use caution.