Download and tile-print the pattern's three pieces, joining the long center piece with a piece of tape.
Pin in place atop doubled fabric, so you're cutting two of each piece. If your fabric has a front and back, make sure the fabric is doubled with fronts together or backs together (to create mirror image pieces).
The starting point for this pattern was based on an aviator cap pattern on DeviantArt!
Use scissors or a rotaty cutter and mat to cut around your pattern pieces. Use tailor's chalk or a water-soluble marking pen to mark the hash lines that are useful for alignment later.
To assemble the cap, first sew the side panels together, then the center piece, then join the center piece to the side panels. Optionally top stitch your seam allowances, and stitch a folded over edge all around.
Add another rectangle of material for a chin strap, if desired.