Hello! So first of all... is this an application portfolio for a certain school? AP portfolio? Just for fun?
The first thing I notice about your art, particularly your graphite works, is that the contrast is low. The first piece and the cola can piece especially are in need of higher contrast between light and dark so that the figures and objects in the pieces are given more definition.
The mermaid picture has much better contrast. Darker tones, great shadow work. I would recommend, for that piece, though, that you try cross hatching your pencil strokes so that not all of the strokes are "skratchy" in appearance, all in one direction.
The composition of most of your pieces is good. The eye can flow well across each piece; again, contrast would improve this even more.
When I got to your first color piece, I fell in love with your color choice. Complementary blue and gold/orange... wonderful! Fabulous use of texture here.
Most of your color pieces are strong, because you add heavy texture to them. The parrot picture could use more contrast and more texture to add appeal to the eye.
Great work so far!