One of the main things you need to improve is making things look as though they are in a 3D space and not on a flat piece of paper.

Look back on the first part of lesson 2 which talks about Thinking in 3D then try to do the organic arrows exercise again and this time make the arrows look more like they are traveling in a 3D world. Give the arrows more depth traveling into the page and don't be afraid to try and do different types of arrows. it looks like you kept drawing the same type of arrow just different sizes.

As for your leaf drawings try to make your contour lines less straight and more curved around the flat form of the leafs next time. Also if you are applying texture to them make the textures travel around the shape of the leaves and look closer at the textures.

The rest looks fine. You seem to understand everything else just keep practicing to make your drawings more accurate.