"Work in progress" - Runensucher's way to [something achievable]

[Runensucher]

So here it is. I'm starting my "sketchbook" now.
Not a lot of creativity will be found in here. I learn the fundamentals step by step while following "draw a box".
So every post is free to all your suggestions. If you wonder who I am - you can read it up here.

First of all I want to show you my first lesson. Here is the link to my imgur album:     klick for art
And you can find my first critique here, if you are interested:     klick for further information


After that I had to draw my 250 boxes:     klick for a lot of boxes
And here is what my teacher said:     klick for more words


At this point I got a little confused. I was told to correct my boxes to learn even more. You may look at this:
Correction to number 57 was straight to the point. But it was just a lucky strike. All other corrections felt weird and they came out even worse. Using the ruler didn't help me. I'm afraid of not getting better with perspective when I can't correct my boxes. I  stopped to correct the boxes after realising that I don't know what to do. Now I feel like I missed an important lesson.



Now let's go to my current work. I'm still at lesson two, and maybe I will stay with it forever.
First two exercises felt pretty normal. But then I had to start with textures:




I'm okay with the results. But what I'm not okay with is that I'm really slow at the moment. I can't draw more than an hour and this includes 15 to 30 minutes of warm up. And yeah... that's why I'm here. I'm in need of feedback and this exercise really feels like working without a goal. So what do you think I could work on precisly?

Thank you for reading. I know I need to take a lot and can't give anything back at the moment. I'm just clueless. :)
But I want to improve and what's even more important to me: I want to stay with it.