First of all, I think you're using a blue ballpoint pen and you shouldn't. You should use a black fineliner with all the exercises (drawabox sells fineliners, they're great and pretty cheap if you live in the US).

You should be more careful about the beginning of your superimposed lines. They don't have a common beginning point and that's a problem. Your ghosted lines have a good trajectory but I don't think doing crosses instead of points is such a great choice. You should draw simple points and not crosses.

The lines of your ghosted planes could be straighter, don't forget to ghost your lines A LOT before marking the paper. The crosses are once again not such a great idea. It gives a messy feeling to the whole page. Furthermore, if you do crosses instead of points in the 250 boxes challenge, it's gonna be a problem. So remember, do small points instead of crosses.

Your ellipses are correct for the most part, however I think you've done to much ellipses sometimes. When you do an ellipse, you should do 2-3 ellipses, no more, no less. On the middle right of your ellipse there's an ellipse that has more than 3 "rounds" and that's a problem.

The vanishing point of your rough perspective is pretty respected, and I think it's gonna get way better as you push through the 250 boxes challenge.

Your rotated boxes exercise is well executed! I think it's a great idea to use the whole page to do the exercise rather than doing multiple pages.