First I measure the area that will be painted. In this case, the interior of the tin was 7" x 23". I use Adobe, either Photoshop or Elements, and open a new, blank file that is whatever the size I am painting, for this 7" x 23". (You could also do this in Word, set the page orientation to landscape and set your margins to be 7" x 23", it would be two pages) Then I either add the text, or image. So in this case I added "WILSON", and tried different fonts, until I found one I liked. Then I kept making the font larger, and larger until it fit in my 7" x 23" box. I took the size number (134 pt.) and then went into Word, typed each letter out on a separate line in 134 pt font. I printed it out on plain office paper, and cut it out with an x-acto knife. (In areas that you might cut the center of the "A", "O", "Q", etc -in this case the loop of the W, I just use small pieces of tape to hold it together.)
I used a dry sponge brush, and acrylic craft paint. To achieve the rusty old look, I layered burnt umber and a spice brown color. I did not mix them, this makes it look naturally worn.
Just dabbed in the letters.
Then I decided it was too dark, so I added a tan color on top.
Took off the paper. And voila!