Draw small U-shaped lines across the base of the animal's neck with a marker. The first line of scales is the most important, as it sets the look for the rest of the reptile's body. Too many or too little scales is not pleasing to the eye, make the scales look lifelike. For a 1-inch-wide neck, you should ideally have four to six scales.
The second line of scales should be drawn slightly off centre to the first. You do not want the scales to line up perfectly down the body; instead, a pattern of mixed lines is much more pleasing to the eye.
Continue drawing the rows of scales in this offset/onset manner until you reach the base of the tail.
As you draw scales down the base of the reptiles tail, they have to become smaller, as they do naturally on a real reptile. As you draw, slowly bring the size of the scales down until the smallest row reach the base of the tail.
Check you work and adjust accordingly. It is never too late to fix a problem while tattooing, as the customer will wear the drawing for the rest of his life.
Using your tattoo gun, "line" your scales. "Lining" is the act of tracing the drawn scales with permanent tattoo ink.
Once the lining is complete, wipe the tattoo clean. Remove the liner needle and attach a shading needle to your tattoo gun.
Shade the scales by making the darkest point of the scale the point of the U, and the lightest point the base. This gives the effect of movement when looking at the finished tattoo. Repeat this process for each scale on the reptile.