You cannot control the sun or the weather but you can still control the lighting. Be aware of where your light source is coming from and where it is landing on your subject. I am going to show you a senior shoot I did at 6pm during the summer. My ideal lighting time. This shot was done in a shaded area so the lighting was naturally diffused (meaning the light is softened before it hits the subject). As you can see from the shadows on her face the sun is hitting the left side of her face. For those times when you don't have the shade of trees building or whatnot, you can always buy some white ripstop (kite fabric) from your local fabric store. You can have an assistant hold it for you or you can build your own frame with pvc pipes from Home Depot or Lowes. This will still give you the shadows but they will be much softer and more flattering. You can even use this fabric at not so ideal times of day to soften the sun. I also like to make sure my background is going to be the same exposure. I don't like to have a blown out background, it is distracting. This image was a long walkway where the lighting was the same throughout. Therefor I got a very pretty well exposed background and foreground. This lighting still gives dimension. You subject looks more 3d than straight on flat lighting.
For those of you that want to know the technical stats:
Camera: Canon 5D Mark II
Lens: EF 70-200mm 2.8L
Exposure: 1/160th of a second at f/3.5
Focal length: 200mm
Here is a pulled out view of my location. Notice the even lighting throughout the walkway. Sometimes tree shade is not ideal because the sun will shine through breaks in the trees, beware of leaf spots...
As for the post proccessing (photoshop) All I did was add contrast and a touch of saturation.
Photoshop FYI: This paragraph may make sense to some of you and may be confusing to others. For all of you anti photo shoppers and photoshop fans... every image needs some sprucing up, even if all it is is a touch of contrast. Each image in your camera is flat. When you take your images straight from camera to walmart's one hour photo, they enhance your images for you. It is an automatic setting with their computers. So, even if you don't use photoshop at home, your printer is using it at the store. I like to have complete control over how my images get enhanced. Then if I choose to go to walmart to print I turn off the color correction. If you do not know how to do this, ask the lab tech and they will show you how. If you enhace your own photos turn off the color correction!! Otherwise all of your hard work goes down the drain. Also, you may ask the lab techs if they can calibrate their printers for you. They are supposed to do this every morning before they open. You may ask if they did and ask to see their log. These are your images, don't be afraid to make sure they are perfect. AND if you are photo shopping your images, make sure you convert your image to srgb. It is a color space that the web uses as well as all one hour photo labs (walmart, target, walgreens, sams club, costco, etc). If you do these things, make sure you have your image as srgb, turn off the color correction at your local one hour photo lab, and make sure the machines are calibrated (just ask), then your images should look like the image on your computer screen. It would be a good idea to get a calibrator for your computer monitor too. That way everything is as it should be.