Sketchbook practice - What should I be drawing?

Drawing progress, en plein air, is always a challenge and a surprise, and the recent weather has proved kindly in allowing me to push forward with some ideas. Even in drizzle I've found trees heavy with leaves which keep the rain off.
Recently I've been thinking about what it is I really want to draw in each scene - where my focal point  is and then trying to make sure all marks support that idea. However its amazing how the pencil keeps running away with itself, and then before you know it the drawing has a life of its own. The thing then is to not let it get away from you too much.

A sketch like this one below kept its focus and didn't become cluttered by too much foreground detail:

...and here the foreground leads into the page:

Good intentions can be harder to control when faced with a view which is less familiar, like this one:

Two things happened with the above drawing which led to it getting away from me completely -Firstly, I was feeling my way around the view, recording too much, not deciding what was important. Secondly, this was compounded by the fact that it was a beautiful day, so I sat and doodled around. My thoughts were clouded by being too relaxed!

The drawing below proves the point:

I didn't have too much time on this one, I needed to get back home. I had to stand and the long grass played host to lots of insects. I could also hear voices in the field next to me and I didn't want to still be drawing when the people came past me. The sense of urgency kept me focused - I just wanted the darkness under the trees to dominate, leading the eye to the path. The negative space became as interesting as the path - I liked the shapes, and I succeeded better in keeping the drawing under control.