The sooner you get started on your portfolio the better.
Most schools require 10-15 pieces for your portfolio, so you should shoot to make 20 + so you can pick the best of the best to submit to admissions.
Generally Admissions at the Top Art Schools want to see originality and skill in each piece. We have a lot of experience with helping our students make the art that gets them in to the top programs, most with scholarships.
If you think you need a little guidance on your portfolio you’re not alone. Thousands of students have sought help here at Ashcan, and started basic and left with a full portfolio of outstanding work.
The sooner you start the better, Enroll Now in the Fall Portfolio Prep Program and feel confident your portfolio will get you in. 
Ashcan Art Blog 