How to Increase in Basic Afghan Stitch
You always make increases in the first half of a row of basic Afghan stitch. Making increases in your Afghan stitch's first row creates extra loops on your hook; then, you work off all the loops in the second half as usual.
To practice making increases, use an Afghan stitch swatch of 16 stitches. To increase 1 stitch, work the first half of the row:
With 1 loop on your hook from the previous row, insert your hook between the first and second stitch.
Don't insert your hook in the vertical bar.
Yarn over (yo) and draw the yarn through the stitch.
One increase at the beginning of the row is complete.
Work in basic Afghan stitch, starting in the next vertical bar, across the rest of the row.
You should have 17 loops on your hook. (Remember, you added one.)
Yarn over (yo) the hook and draw your yarn through 1 loop on the hook.
Make sure you draw it through only one loop.
Yarn over the hook and draw your yarn through the next 2 loops on the hook.
Repeat this step across the row until 1 loop remains on the hook.