Often what makes a professional photograph stand out from a novice's is the lighting. Be aware of where the sun is if you're shooting outdoors. You don't want to take photos with your subjects directly facing the sun. Yes, they'll be well lit, but they'll almost certainly be squinting and that doesn't look good either. Diffused light is the best for most animal and people shots, because the subjects aren't called out in harsh relief and shadows are muted.
Fill flashes are a really useful tool. With a fill flash, you can photograph subjects with the light source behind them and their faces won't be in shadow. And on days when the sunlight is filtered by clouds, a fill flash can highlight things that the more muted sunlight would miss.
Product shots should have good strong lighting. If you want the effect of shadows in your image, using a strong light source on your subject will help develop them. It is always possible to add them in later with Photoshop, but that can look unnatural unless you're very careful. Besides, the less post-processing that you have to do the better - if only because it's less work.
