It takes practice to learn to identify which information in a scene is essential and which is optional. Then it takes even more practice to let go of the optional bits. The job is made easier by warming up with a very quick sketch. I like to start work on a new subject with a "five minute painting".
Putting a radical limit on how long you spend on your first sketch means you haven't got time for details. When you have no choice but to see the scene in very general terms the big shapes emerge as the fundamental structure.
You can often find the "bones" of a scene by looking at the relative values of the shapes.
In the image below there are just a few major shapes. Start with the lights; sky and road. Then the mid-values; the buildings visible under the elevated highway and in the distance, and the darks; the highway and the shadow it casts. If you have time you might add a car or two, and a few windows, but even without any details the essence of the scene is there.
A large part of letting go of detail or texture involves giving yourself permission to treat subjects approximately. In the image below the white crane presents the familiar problem of reserving specific lights while applying a clear wash. Trying to paint around those skinny white lines without compromising the fluidity of the sky wash is enough to get you reaching for the masking fluid! But with only five minutes, you haven't got time to wait for that stuff to dry. Instead, you can let go of getting the crane to be correct, and simply do the best you can. Relax your standards. It's not a painting, it's an approximation.
If you were painting from the photo below, it would be understandable for you to work to keep the buildings separate from each other by letting the paint dry on one before painting an adjacent shape.
This would be impossible in a very quick sketch. You would have to accept that the buildings would flow into each other. The good news is that you would get to see how the buildings look when you give the paint lots of room to run. If the sketch starts to get dry you could give the buildings more definition with the darkest darks, like the outline of the gable on top of the yellow building and the windows of the white one.
A few more...