Separate the navigation signs you see into categories. Navigation signs are either regulatory, warning, destination or informational. Regulatory signs impact the flow of traffic (e.g., a yield sign, traffic lights). Warning signs indicate an upcoming hazard, while destination signs give route numbers and directional information. Informational signs give data on distance and the location of points of interest.
Note the color of the signs. The color of the signs will differ based on the information they provide. Red means stop, yellow means proceed with caution and green means go for traffic lights. Yellow signs usually are hazard signs. Green signs are usually destination signs, information signs usually are white or blue and regulatory signs typically are white.
Visit the website for the Department of Motor Vehicles in your jurisdiction (see "Resources"), or visit an independent traffic signs website such as usatrafficsigns.com. Take the online tests available and review the sign material on these websites. Alternately, obtain and study a basic driver's training booklet from the DMV, as the booklet should indicate the meaning of basic traffic signs.
Accompany an experienced driver on a road trip. Point out the signs you see and have the driver quiz you on their meaning.