A yard sign is not a poster, a flyer or a billboard. It is read at speed, from an angle, by somebody who was not looking for it. Every design rule below comes out of that one fact.
Count the words
The practical ceiling is about seven words on the whole sign, and fewer is better. A name, a category and a phone number is a complete sign. Adding a slogan does not add a message; it shrinks the message you already had.
The test: read your draft aloud in two seconds. If you cannot, it is too long — not too small.
Contrast beats colour
Legibility at distance is about the difference in lightness between the type and the background, not the hue. Dark navy on white reads at forty feet. Mid-blue on mid-red does not, however good the brand guide says it looks.
If you must use two brand colours of similar lightness, put one of them on a white field rather than against the other.
Size the phone number, not the logo
The instinct is to make the logo dominant. On a lawn sign, the number people need to act is the thing that has to be biggest after the name. A logo that reads at ten feet and a number that does not is a sign that generates recognition and no calls.
Kill the website and the QR code
Nobody types a URL from a moving car and nobody scans a QR code from one either — the scan needs the driver to stop, get out, and hold a phone steady at a sign in a verge. Put the URL on the van; put the number on the sign.
What we do about it
We lay out every order before you pay, and where we think the design will not read we send a second version alongside yours in the same free mockup. You still choose. You just get to choose having seen both.