Develop the habit of always working with the same lens first to avoid mix-ups.
Remove the lens from its container and examine it to make sure that it is moist, clean, clear and free of any nicks or tears. If the lens appears damaged, do not use it. Use another lens. Verify that the lens is not turned inside out by placing it on your forefinger and checking its profile. The lens should assume a natural, curved, bowl-like shape. If the lens edges tend to point outward, the lens is inside out. Another method is to gently squeeze the lens between the thumb and forefinger. The edges should turn inward. If the lens is inside out, the edges will turn slightly outward.