When drawing the squares, make an effort to keep the lines lighter as they're really guidelines for the circle drawing. Take the time to get the squares right; you may want to draw just the squares then go back and draw the circles afterwards instead of drawing a square then popping a circle inside then drawing another square. You should be drawing consistently good squares at this point as wobbly shapes or rectangles don't allow you to make good circles.
Break the squares into bite-sized portions when starting (dividing the square into quarters as demonstrated in exercise #1 is perfectly okay to start, but you do want to move towards drawing without too many guides). Lightly indicate the curved arc moving from one side to another then continue into the next quadrant. If you're working on a table, feel free to rotate your sketchbook as you go. If the circle seems to wander into diamond-shape territory you can lightly draw in the corner-to-corner diagonals and measure a half-inch from the centre and make a tick-mark. The circle is an inch in diameter no matter what point you slice it in half, so this gives you another guide to work with until you're comfortable with the circle.
A circle is essentially a sphere without any depth added. When we get around to perspective we'll discuss how to draw those oval "ellipses" accurately, but, I think it's important to show where any exercise leads to later on. Since a circle sits exactly inside a square, it's not a great leap to understanding that a sphere fits inside a cube in the same way.
All these simplified shapes do lead to even more complex construction, like Loomis's sphere method for sonstructing heads, but you really need to have control of the basics so that the end result turns out how you want it to.
Like last week, spend 10-15 minutes of the exercise portion of your daily sketchbook drawing, then another 15-20 minutes drawing anything anyway you like. Of course, spreading the exercise and other drawing over the course of your day will make that half-hour seem like no time at all. Next week I'll be adding another, slightly more difficult step.
I hope all of you are having a great holiday season!