From Tie-dye Wiki
The lightning bolt is suitable for lighter fabrics, since it consists of multiple folds resulting in many layers. First fold fabric in half. Perpendicular to the first fold, do a few wide "spread accordion" folds. (Spread accordion folds means fold up in 1/2 unit length, fold down in whole unit length). Then fold the whole pack diagonally in accordion manner and apply dye perpendicular to the last accordion fold.
Here is an example of a Double Lightning Bolt
How to fold the double Lightning Bolt:
Step 1. Lay dampened shirt flat, face down. Smooth out any wrinkles, and align seams.
Step 2. Fold shirt in half vertically, again smoothing out wrinkles and aligning sides.
Step 3. Starting about the middle of the chest, fold shirt up to about the bottom of the sleeve.
Step 4. From about half-way between the bottom of the fold and the hem of the shirt, create another fold and bring it up to slightly overlap the first fold.
Step 5. Using a straight edge and a washable fabric marker, draw a diagonal line from a point between the neck and the sleeve to just above the hem.
Step 6. Starting at the bottom of the diagonal line, form accordion folds keeping the line straight as you go up to the shoulder.
Accordion folds will be bulky due to the thicknesses of the horizontal folds.
Step 7. Use cotton string, sinew or rubber bands to secure the accordion folds from the line over toward the sleeve.