One of the simplest ways is to make a lens test chart by finding a suitable flat vertical surface (wall, etc.) and taping 5 newspaper pages to it in an X pattern so that you have one in the center and one at each corner of your picture as viewed through your camera at a distance of 12 feet or so (the distance is arbitrary, 12 feet is just a compromise between close-up and distant). Photograph this on ISO 100 film or slower and then examine the results at a reasonable magnification (magnifying glass, loupe, slide projector, enlarger). You will immediately see whether the newspaper type is sharp or not. Expect reasonable sharpness at full aperture in the center, getting better at small apertures, and less good sharpness at the edge at full aperture, improving to almost or fully match the center at 3 to 4 stops smaller than maximum.