In order to prepare an image (design, graphics, illustration, photography) for screen printing, one need to understand a little bit how this method works.

The silkscreen printing method (or by the name: screen printing) allows you to print the same image multiple times on different materials and with different colors. The image is transferred to the screen mesh so that you actually create a durable and strong stencil on the mesh. The mesh is very dense, tense and connected regularly to the frame of the screen.

Now note that the image is transmitted to the network by means of a photographic emulsion, a type of light-sensitive liquid that is applied in a thin layer on the grid. When the emulsion has finished drying completely on the grid it works as follows: When it encounters light it becomes difficult and becomes waterproof when it is kept in a dark area it easily falls under water. Therefore, in order to create the image on the mesh the image area should be blocked so no light can get through. You do that by printing the image in black-opaque color with a simple home printer on a film. Using a dedicated light table or projector to expose the screen to light with the black image printed film on it. After it exposes the image will wash in water: the result on the mesh is negative of your image. 

The image you're going to make as to be black! Only a black, opaque and strong color will succeed in blocking the light and allow the emulsion behind it to come down and reveal your illustration on the mesh. Therefore it is not desirable to create an image with many small dots or many thin lines.
You must save the file to its real size, the size you want it to print on your screen. * If you send me a file to print, note that I can print up to A4 size. For printing on a larger film, you can contact a Printing Institute.
Save the file as a 300 dpi DPI. It is recommended to use Photoshop or Illustrator, if you have no idea what it is and you need help please contact me and I will be happy to help, talk to me.
Want to do a job with a few colors and do not understand how to prepare the file? I wrote a post about four-color printing, hoping that the explanation there is satisfactory. If there is still a problem, write to me.

* This is suitable for everyone and is specifically intended for participants in my screen printing workshop. See what this is about.