For my test exposure, I used an old piece of work with heavy line work. In photoshop, I added time markers, which will make sense when you see them in action.
Ideally I would have my image printed on acetate, but this can run quite expensive. A cost-effective way of doing it, and the method I have always used, is to print the artwork onto basic printer paper and oil it up to make the white transparent. I have used baby oil (because it smells nice!), but cooking oil works just as well. When the paper is fully coated, blot away all the excess oil using some scrap paper. Newspaper is fine, but be careful that the ink doesn't transfer.
Now, for exposing the image, my equipment was layered as follows:
1. A black foam base
2. My coated screen
3. My artwork, right-side-down
4. A sheet of glass
The black base is to stop the light from scattering, and the glass is to keep the artwork still, and close to the mesh. The board you can see in the image is what I used to cover each section of the artwork at 10 minute intervals, to gauge what exposure time is best. After 40 minutes, the screen was thoroughly rinsed down with a hose, to reveal the burnt-on artwork.