Good question, Dave.
There are a lot of ways I could have answered, Dave, but I concentrated on a few basics. Here’s how I suggested he get a nice blue sky in his photographs.
1. Pick a bright blue sky day. Cloudy days (particularly hazy, gray, overcast days) are really difficult to make blue skies. Start with a blue sky day if you want to make a blue sky photograph. It’s not rocket science, but a lot of folks shoot themselves in the foot by trying to do something practically impossible. If it’s rainy, sleep in and try for tomorrow.
2. Choose at a time of day when the sky is naturally deep blue. This could be close to sunrise if you’re facing west, or in the darkening eastern sky toward sunset. Basically, point your camera in the direction opposite the rising or setting sun and you’re sure to find deep blue. In the middle of the day you’ll find the deepest blue sky with the sun slightly at your back, too. Unless…
3. Shoot with a polarizer. Putting a polarizer on your lens will automatically deepen the color of a clear blue sky. There’s actually a bit of a formula for this: the darkest blue sky will be achieved 90 degrees from the sun. That means point your camera in the direction of the sun, then turn directly left or right: that sky will be darkest blue. Watch out for graduated blue skies from polarizers, though. At just the right angle—say 120 degrees from the sun—you might see a deeply polarized dark blue sky on one edge of the frame and a light blue sky on the other. If it’s distracting enough you may find that no polarizer actually looks better. The sky might not be such a dark blue, but at least it will look natural.
4. Underexpose slightly. It will ensure the sky is a rich royal blue hue, though if you have shadows with detail in the scene you may lose them. If true underexposure seems a little scary, why not try shooting RAW and darken the exposure to deepen the blue sky in the RAW file conversion. (While you’re at it, you can add a vignette or exposure gradient to darken the blue sky even further. What? That’s not cheating. It’s not a Photoshop fix if you do it with Lightroom!)
5. Use manual white balance. Auto white balance can sometimes render colors slightly off or even washed out. With a preset (such as, hmm, I don’t know… maybe DAYLIGHT!) or even a custom white balance, you’re sure to maximize your chances of a true-to-life bright blue sky. If you want to cheat a bit, white balance on something a little too warm to make everything in the scene a little too blue—like the already blue sky. Sneaky!