Here's how I made a couple sheets for a Graco Pack 'n Play ...
Materials (for one sheet)
1. Fold the fabric lengthwise and width-wise.
2. Measure and cut a 3-1/2" square from the corner (when unfolded, each corner will have a square cut out).
3. Pin and sew each corner right sides together. I used a 4-thread overlock with
integrated safety seam on my serger; however, a straight stitch on a sewing machine will do.
4. Serge or zig zag stitch around the edges to prevent fraying when laundering.
5. Iron over 3/4".
6. Mark a stopping and starting point about 1" apart. I used flower head pins.
7. On a sewing machine, straight stitch about 1/4" from edge (for me, this was along the serged stitch) from the start marker to the stop marker leaving about a 1" gap to insert the elastic.
8. "Thread" the elastic through the opening. I've seen some use safety pins, bodkin needles, etc. I haven't had much luck with safety pins and do not own a bodkin needle ... so I improvised and used a bobby pin. To use a bobby pin, simply cut a teeny, tiny slit in the elastic about an inch back to thread the bobby pin, like so.
9. Now that the elastic has been threaded, zig zag stitch the two ends together.
10. Straight stitch over the gap to enclose the elastic.
Inspired by TUTORIAL: Crib and Toddler Bed SHEETS