You can free hand a pattern or use one of your favorite tanks as a guide.
Trace front; flip and trace back. Cut out.

Front back cut outs

Measure length of neck line
(front only) Shoulder to shoulder.
a. Note: you can adjust the neck line (shape) to your liking; I made my neckline a little bigger. If you are tracing, do not measure the guide. Measure the fabric cut out neck line.
b.My new neckline measurements were 20 inches. I wanted the fringe to 9 inches long. So my fabric for the fringe cut out was 25” x 9” (always cut out more than you need just in case, excess can always be trimmed in the end).

Measure fabric for neck fringe remember: always measure 3-5 inches more in length just in case. This can always be trimmed later. Cut out.

3 pieces: front, back and neck line for fringe.

Flip wrong side out and sew sides of tank

Flip right side out and place neck fabric on top of neck line, and then sew together around entire neck line. cut any remaining fabric
Sew two rows.

Start cutting the neck fabric from bottom to top to create fringes. Do not cut too far up or too close to the thread of the neck line.

When finished cutting all the fringes, Flip wrong side out again and sew tank straps together.