So, if I understand correctly, you've just completed your undergrad degree in computer science. Your scores are average, but your GMAT is off the charts (congratulations!!). You have no full-time work experience since you've just graduated and you've not got much in the way of strong leadership stories. This is a tough one!
There are some programs that will consider candidates that are currently in undergrad, but it sounds like you've completed your studies. In any case, even these students have to demonstrate exceptional leadership capability through robust internships, active leadership roles on campus and off, etc. I don't see a lot for you to stand on in this area, so my advice would be, if you want to go for a top 20 school, go work for 2-3 years first. During this time, focus on building a career that ideally is on the business side (vs. becoming an engineer), try to work at a big MNC (HSBC, Deloitte, etc.), and also focus on building up a strong leadership profile outside of the workplace. Since you love movies/script-writing, maybe you could try to produce an independent film (maybe that's a bit ambitious!). Or you could build a non profit production company that hosts free plays for underprivileged communities in India. Be creative and really think build up your profile in these ways (these are just ideas - do what you're passionate about). You'll want to show:
Very strong professional leadership capability (teamwork, firm stewardship, taking initiative, consistent promotions, etc.)
Very strong leadership in the community (start a non profit, take a board position on a non profit you're passionate about, regularly volunteer at a nonprofit and work your way to a leadership role there)
Very strong extracurricular activities/engagement - want to demonstrate leadership here, too (produce a blockbuster film (hehe)
, captain a football team, etc.)
Very strong academic achievement - you've already done that!
Your GMAT score will be valid for 5 years from the date you took the test, so no worries on that front. But waiting one year won't give you enough depth of experience to be competitive at a top tier school. You'll need to take the time to develop your profile in all these different ways, and then you're application will be very strong.
Of course, you can always try to through in an application now (it's not going to hurt you if you get rejected now -- you can simply reapply when you're ready), but I don't think your chances would be very strong at a top tier school, even despite your GMAT.
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