Regarding warm-ups, as mentioned here, it's best to do them before every drawing session.

As for the critique, for the first 50, your lines are clean overall, with very little arcing or wobbling present throughout the set. Your convergences also show good accuracy, though I did see a few lines veery off in the wrong direction, like in box 10, box 30, and box 45.

For the next 50, your lines remain clean throughout the set. As before, I noticed very little arcing or wobbling. Your convergences also show improvement in accuracy, with fewer errant lines. However, I did see a few lines pair off and converge towards two vanishing points, like in box 59, box 76, and box 95.

For the last 150, your lines remain clean and even throughout the rest of the challenge, demonstrating very good technique and consistency. Your convergences also continue to improve, though there are still instances of lines pairing off, like in box 107, box 167, and box 233. In these boxes, the inner lines (green and orange in this diagram) diverge instead of converging at the vanishing point. Keeping in mind the angles of neighboring lines can help when planning the box's construction.

As an aside, some of your boxes are missing some line extensions: box 2, box 14, and box 17. Also, box 72 has some lines extended in the wrong direction. It's not a major issue since it didn't happen often, but I want to point it out for future reference.

All said, you did very well. I'm going to mark this challenge as complete.