Those instructions are too aimless. They're right to start you off with exercises that build your ability to control the pencil, but you also need to be developing specific skills like drawing straight lines, C curves, S curves, and later, ellipses. These are the basic components of all flat shapes, and all forms in perspective. Of course you can doodle as much as you please in between your focused sessions.
Your goal for now should be to get the pencil to do what you want it to do. Go to DrawABox.com and spend a lot of time on the earliest exercises. Drawing straight lines point-to-point with the ghosting technique, drawing multiple intersecting straight lines through a single point, drawing arcs through a series of points, and accurately drawing over any of the lines in these exercises multiple times. Do these whenever you have a spare minute.
The purpose of all this is grow comfortable laying down the lines and shapes you'll need to draw from life. You shouldn't even begin to worry about accurate measuring, correct angles, or anything else until you can handle a pencil or pen without having to try really hard to keep it under control.
The basics you should learn, in this order, are:
1) Clean and accurate straight lines (parallel and intersecting), C curves, and S curves
2) Clean and accurate squares and ellipses
3) Clean and accurate basic forms in 1-point perspective (always drawing through a form as though it's a wire frame model or a glass paperweight): boxes, cones, pyramids, cylinders, spheres (with an ellipse on the horizontal axis, and another on the vertical to get your 4 hemispheres, which define the sphere's orientation in space)
4) Contour line practice on the basic forms mentioned above, and also lots of random squishy blobs with bands and nets of contour lines all over to give a good firm sense of their shape and weight. (DrawABox.com has lessons for this, and the later lessons show you how to apply the forms and blobs to drawings of actual things.)
This might sound like a lot of tedious nonsense, but it's super important to nail this stuff down so you can draw from life without struggling with the basics. Trust me, you can waste a lot of time if you skip ahead without putting in the work to figure these things out.
Once you get your hand trained and you're good at drawing lines and forms, drawing real things befomes a relatively straightforward matter of building objects out of basic forms and then sanding down some edges and softening plane breaks where appropriate. You work out the scaffolding, then layer on some surface finish that conforms to the contours. But good line drawing is really about good construction.