My table is small -- a 36x48" oval -- so I didn't need a lot of fabric. I think I bought about a yard and a half. I started by draping the fabric, wrong-side-down, over the table. I used a pencil to trace around the table's edge then cut, leaving 1/2" for a seam allowance.
To make the cover fitted, I cut a long strip 6" wide and sewed it around the edge of the table-top piece. I graded and notched the seam allowance (to reduce bulk) then edge-stitched around the top so it'd lie flat.
Finally, I sewed a 1/2" hem around the bottom.
Ta-dah!
I love it, and it was so easy to make!