A cracked screen on your Android device is unsightly, can be dangerous to your fingers, and can even cost you a date, but there are more than a few ways you can deal with the issue to keep your sanity - and your phone - intact. Starting off with the cheapest solution, if the cracks on your device aren't obscuring the viewable area and your phone isn't one of the ones that can no longer accept touch input or experiences erratic touches when cracked, like some Sony or LG devices, putting a glass screen protector on the device will make for a much smoother user experience, and may even help the aforementioned crack-sensitive devices to function. Naturally, a sturdy case is probably a good idea, as well. If you have some cash and are looking to get your device fixed, the way you should go about it can differ.
If you purchased a carrier warranty with your device and the device is fairly new, check prices on the carrier and manufacturer warranties. The manufacturer warranty will likely cover a wide range of damages and defects, and will ship your device back with your warranty and any waterproofing still intact. Some manufacturers also offer optional device protection that's more comprehensive than other solutions, such as HTC's Uh Oh Protection. In many cases, the carrier warranty will be cheaper because you're paying for it. Your carrier warranty can have different pricing and policies, such as how many claims you can make per year or what types of damage are covered. Some carrier warranty plans won't cover accidental damage, depending on their level, so be careful when buying them. You also won't be able to just up and enroll in the carrier plan when your device breaks, so it may be a smart idea to get on the plan when you get your device, if you're clumsy. If you didn't sign up for the plan or didn't get your device through your carrier, there are other options.
If you got your hands on a somewhat older device, an imported device, or a cheap device that was a bargain because you bought it broken, you won't be able to indulge in the manufacturer or carrier warranty in most cases. Should this end up being your situation, you're not always stuck paying out hundreds; some third party repair shops are far cheaper than others, so always shop around in your area. If you'd like to DIY the repair and your device isn't eligible for a manufacturer or carrier warranty, you don't have much to lose, as long as your skills are up to par. Many modern devices require melting glue on the face with a heat gun before prying the glass off, which can be incredibly difficult. Do your reading online, ask others, and make sure you have the right tools. To melt glue, you'll need a heat gun and a laser thermometer. Other devices may be somewhat simpler.