There are a few possibilities here. By far the most common cause of cracked lips is exposure to irritating conditions, such as wind and cold. This is pretty common in certain occupations and hobbies, regardless of the time of year. For example, if you are an outdoors runner, your lips may dry out even in the summer. Similarly, if you have a habit of licking your lips, this will contribute to them drying out. In order to prevent this, you should make certain to apply chapstick frequently to keep the skin on your lips well lubricated. Avoid picking at the dry skin or licking your lips, as this will just worsen things. Make sure to use a chapstick with sun blocker in it if you will be out in the sun, as UV rays can also make the problem worse.
If you have cracking of the lips that is mostly at the corners of the mouth, rather than evenly all over the lips, then this is a different condition called angular cheilitis. Angular cheilitis is sometimes a result of a nutritional deficiency but is usually related to a fungal infection. Ask your primary care doctor
about it, as they can prescribe medications to clear up the infection.