Anything marked as freeleech (e.g., the staff picks on the front page) that you download will have no negative effect on your ratio, but you still get upload credit from seeding it. All the freeleech stuff really helps boost your ratio because it's basically free upload. If you have the HDD space then you can download every format (V0, V2, FLAC, AAC, etc) of each album on freeleech for even bigger returns with no penalty.
When I was new and trying to get a good buffer I'd just leave my computer on 24/7, seeding everything that I'd ever downloaded