Determine the size bag you want. Spend an hour digging through all your precious fabrics looking for just the right one and dreaming of what else you can make. Change your mind a few times as you find the piece you chose isn't the right size. Decide to make 3 bags instead of one. (This is how I sew, anyway! LOL!)
For the bag I made, my print is directional, so I'm cutting the fabric into two pieces to make the print face the same way on both sides. (The shape of my scrap piece wouldn't allow me to fold it and keep the print facing up on both sides of the bag.) See under this post for different ways to cut your fabric.
Materials:
Fabric, Cut 2:
Width: finished size + 1" (for two 1/2" seam allowances)
Length: finished size + 1/2" bottom seam + 1" casing
My example: width: 10" + 1" = 11"
Length: 14" + 1/2" + 1" = 15 1/2"
So I cut two pieces that are 11" wide x 15 1/2" long.
Drawstring: BTW, I don't measure the drawstring. I just insert it, tie it close to one end, and cut off the extra. You'd need enough to go around the diameter of the bag + several inches to make a knot, so possibly 20" + 6" minimum for this bag.
1. Serge all raw edges. This is to finish the edges, so trim off very little, and do NOT serge any sides together.
2. Place fabric right sides together. With your sewing machine, sew bottom and sides using a 1/2" seam allowance. If your print is directional (has a definite right side up), make sure it will be right side up on both sides if desired. On one side, stop 2 1/2" - 3" from top of bag. This is where your casing for the drawstring will be.
3. Press side seams open all the way to the top (including part you haven't sewn).
4. Top stitch the unseamed sides close to the edge. Start at the top of the bag, sew to the seamed section, and turn around to sew the other side. Will look like a "V".

Steps 3 and 4.
5. Fold the top of the bag down 1" wrong sides together and press.
6. Lay the drawstring near the fold, so it'll be in place while you sew the casing together. Top stitch the casing down close to the serged edge. Turn bag right side out.
If you're not comfortable sewing the casing with the drawstring inside, then topstitch casing without the string inserted. Turn bag right side out. Then, insert string using a safety pin stuck in it to help guide it through if needed.

Steps 5 and 6.
7. Optional: put a bead or toggle on both drawstrings. Make sure they hold the bag in place before tying the string. (If the bead hole is too big, it'll just slide down the string instead of staying in place.)
8. Tie string and cut extra off the ends.
Alternative ways of cutting fabric:
For cutting one piece of fabric and folding left to right:
Width: finished size + 1" seam allowance
Length: finished size + 1/2" bottom allowance + 1" casing
For cutting one piece of fabric and folding bottom to top (if your print is directional, this method will result in one side being upside down:
Width: finished size + 1" seam allowance
Length: finished size + 2" casing (top and bottom will be the casing)