4:23 PM, Sunday July 25th 2021
Hi! So while your lines look like they could definitely use some practice, it's pretty normal to have lower than usual quality lines on this exercise in particular. The lines used here are shorter than the ones used in other exercises, and you're drawing a box, that tends to give everyone (myself, back when doing this exercise, included) to over-focus on having the lines reach their endpoints instead of confidence. I do recommend practicing some ghosted lines to get them better, especially shorter ones, but high line quality is really not required at this point in the lessons.
To answer your question, the best way to distinguish the horizontal and vertical lines representing the front face of the box and the side lines representing the depth lines of the box is just that: the horizontal and vertical lines should be parallel or perpendicular to the horizon, while the depth lines should not be (and are hopefully going towards the vanishing point). Now, from your work, I can see that not all of the lines that are supposed to be horizontal or vertical are, but with a closer look I can tell pretty well which ones are meant to be horizontal and vertical, and which ones aren't.
Hope this helps!
9:56 PM, Sunday July 25th 2021
Yeah, I know. I am hardcore :-)
2:35 PM, Sunday July 25th 2021
From looking at your work so far I would suggest that you need to just do one exercise everyday. That is drawing straight lines point to point, using ghosting. Do this every day filling up a page of A4 at least.
Your lines at the moment aren't good enough to make the subsequent exercises useful. They are too wobbly and sketchy. Once you nail that, then move on to the next one.
Pace is a thing that isn't often mentioned, but trying to rush through without nailing the basics to a good standard just means that problems compound. Take your time but practice everday if you can. Compare your lines to some professionally critiqued submissions and see how they compare. Not expecting that your lines should like like they are drawn with a ruler but they should be getting reasonably close before you move on. IMO.
9:58 AM, Monday July 26th 2021
Straight lines or ghosted planes would be suitable. The goal is to be able to draw straight lines from point to point confidently. Yours tend to taper and veer towards the end, almost like you are flicking your pen rather than maintaining that control and confidence. The perspective exercises depend on being able to read a straight line to a vanishing point.
I don't want you to get bored but it is well worth trying to get good line accuracy before tackling complex exercises like rotated boxes.
7:01 PM, Sunday July 25th 2021
Just to add to what have been said, take a look at a window in your room. That is the front face of your box. Can you see how two lines are parallel to the floor, while the other two are perpendicular? It is the same on the page. From the four corners of the window, four lines converge toward the VP. Connect those four lines to create another face/window on the page, just smaller. At what distance it's up to you to decide.
Among the wild ones there are also some good lines, I think you just need to take your time with the ghosting method.