Invisible Cities (creative work) - Photoshop Brush Exercises

Started using Photoshop today, here's the result. I found the second exercise quite difficult to start with, using the marquee and lasso tool to create the thumbnails. However I can see the benefit from using these tools so I plan on trying to use them more for my next batch of thumbnails. I ran out of time on the third sheet so it's a work in progress which I will finish off very soon.

Any and all feedback is welcomed!