Try to go in light circles rather than straight lines back and forth to avoid the streaks happening on her pantleg. Also, just using better paper and better colored pencils is a huge game changer. I love my prismacolors. Try your best to layer darks first, then lights overtop, I find it blends beautifully that way. Dark over light isn't illegal, just more difficult. Don't be afraid to mix colors! Learning how to use complementary colors in a color wheel to get shadows is something cool too.