Purchase a premade henna paste from a hobby store or body art shop or ask for a recipe and purchase the powder necessary to make the paste yourself. It is important that you always use a fresh henna paste, as the ingredients are natural and can spoil, causing skin irritation and possible infection.
Locate an image of a guitar that you are interested in. Consider where you want to locate the henna tattoo on your body and use that decision as a guide for the size and shape of the artwork that you would like to create.
Purchase carbon copy paper and a transfer pencil at an art or hobby store. Trace the image of the guitar to the carbon copy paper. Apply a petroleum jelly to the part of the body where the tattoo will be located and place the carbon paper with the design to the jelly to transfer the image of the guitar onto your skin.
Go over the pattern with a paintbrush using henna paste. Allow the paste to dry based on how long you want the image to stay and how dark you want it to be. The longer the paste sits, the longer the image will stay.
Brush away any extra dried henna paste. Notice that the image will darken for a few days and likely stay for as long as a few weeks.