Inspired by these two pictures I found online (and partly this tutorial by Annika of The Pineneedle Collective), here's how I made this simple cotton smock dress.
I used about 1.5 yards of a gray knit (pre-washed), and it only took a few hours, since the shape of the dress is very simple and fits very loosely.
To start, I made the body of the shirt using a loose fitting crop top I own for reference, adding a few inches around the edges for seam allowance and adjustments. I traced around where the sleeve seams were to make it a tank top shape, and adjusted the front and back necklines. Since the back piece was cut into two pieces instead of one like the front, I added some width to it, and then sewed the middle seam to connect the two. (I mostly just did this because I laid my fabric out weirdly and it was just easier to cut it in half.)
I then attached the front and back pieces along the sides and shoulders, and then tried it on to adjust the width and length (I find it easier to make it bigger at first and then adjust instead of trying to make it fit from the start in case it's too small).
For the skirt, I cut the widest piece I could from the fabric to about 17 inches (later shortened to about 15 inches since I'm short) and gathered the top edge by sewing a long basting stitch along the top edge and gathering it to match the size of the opening at the bottom of the shirt. I then connected the two ends to make a tube with the top of one opening as the gathered edge.
With the skirt wrong side out and the shirt right side out placed inside of the skirt, I attached the skirt to the bottom of the shirt using a straight stitch all the way around.
For the sleeves, I used the opening of the armhole as a template for the sleeve, and cut it so that the top of the sleeve was on fold. I first hemmed the edge of the sleeve using a rolled hem, folding it under twice, and then connected the bottom edge to form a tube shape.
To attach the sleeve to the armhole, I matched up the top of the sleeve with the shoulder seam and pinned along the opening, starting and the top and working down the each side towards the armpit area. It's easier to make the sleeve diameter bigger than needed, since my sleeve was slightly too small and I think it would've been easier to have a too large sleeve and then adjust the size down instead of trying to make a small opening match up with a larger one.
I finished the dress off by hemming the neckline in the same way I did on the sleeves, and then hemming the bottom edge by folding it under twice and sewing two straight lines around (sort of like what you see on the bottom of most shirts).
I later added some white lace around the neckline only on the front which I bought at Joann which I sewed on by tucking under the folded neckline.