It's a fact that your concrete driveway is going to develop cracks. Water is a vital component in mixing concrete, and water, even when mixed in concrete, evaporates over time. As it loses moisture over the course of many years, the concrete shrinks, and cracks form. The grooves that are cut into your driveway or sidewalk are actually installed as a deliberate point of weakness so that when the inevitable occurs, the cracks develop in those grooves, and are more or less invisible. But despite that effort, most driveways develop visible cracks in other places as well. When they form, be proactive about patching them. If you leave them alone for just a single winter, during which water to seep into the cracks and then freeze, expanding, the cracks in your driveway will grow exponentially in size.
For best results, wait for weather in the mid-60s or cooler to install your concrete patch. If it's too hot, the water you add to the concrete will evaporate before the concrete achieves maximum strength. But don't do your repair when it's too cold. Concrete needs water to cure, not ice, so make sure freezing weather is not imminent when you patch your driveway.
It's important to get any dirt and debris out of the driveway crack before you patch it. You also want to make sure your patching compound can get all the way into the crack, so use a hammer and chisel or screwdriver to widen any narrow parts of the crack, paying particular attention to the ends, where it tends to taper. You want a minimum width of 1/8 inch to work with.
When mixing your patching compound, keep in mind that the mixing instructions are really more of a guideline. Begin by adding about 25 percent less water than the instructions call for. Mix, then evaluate the consistency. You want it wet enough so that it will pour like a liquid--but just barely. Add water until you achieve this consistency.
The area where you're installing the patch should be damp before you apply the patching compound. Use your finishing tool (a block of wood works if you don't have a trowel) to work the compound deep into the driveway crack, and then smooth it out. Don't worry about making it perfect--the repair will be visible no matter what you do. Your driveway will still look much better than it did. The important thing is simply to make it smooth to the point that it's flush with the rest of the driveway. Cover the repair with a sheet of plastic (garbage bags work well) and leave it covered for at least three days. If there is rain in the forecast, make sure the plastic is weighted down tightly enough so that no rain water can get in.
Again, your driveway will develop cracks over time. But if you patch them as they occur, you won't have to worry about one crack leading to many, many more.