1. The Middle of the Afternoon: Many photographers do everything correctly when making an image but shoot in the harsh mid-day light. As you can see the image on the left is technically fine except the lighting conditions are not helping to bring out it's best.
2. Soft Light: Soft light is often easy to shoot in because it's easy to get good exposures, not having to deal with big differences between highlights and shadows. However, sometimes soft light can make bird images appear soft or they may light the vibrancy of a highlight.
3. Back Lighting can add an interesting rim light to your subject. However, it can often make the front of the subject too dark. You can improve these images by using reflectors or lights to fill in the front of your subject. In the image below (left) I didn't use a fill light, but I was able to recover some exposure on her face through post processing.
4. Warm Vs. Cool Light: There is nothing wrong with either type of light. They each tell a different story.
5. Front Vs. Side Lighting: Both of these can make great images, just be aware that front lighting can be boring due to a lack of transition from highlights to shadows.