I often advise folks to use Manual Exposure if their camera has that feature. Manual Exposure gives you the most control over the exposure (lightness or darkness of your images). At first it seems intimidating, but it is actually easy to learn and after you have used it a few times, you probably won't want to go back to using any of the automatic exposure modes like Aperture Priority.
We created a short video tutorial to show how to set the exposure manually on a digital SLR camera. In this case we used a Canon Digital Rebel T1i, but the procedure is very similar for most other digital SLR cameras. The only difference is that the dials and buttons might be located in different locations. Below is the YouTube version of the video. It's not the most professional video on the web, (we are product photographers; not videographers) but hopefully you will find it helpful. Your feedback is welcomed: