As a starting point, it is useful to know where you want to position your subject in relation to the lighting. There are three different options: front-lighting (positioning the light source behind the camera), side-lighting (positioning the light source at an angle to the subject), and back-lighting (positioning the light source behind the subject).
Most photographers start out using front-lighting, but there are some obvious downsides to this that become evident when you view the results. First, if you are photographing people and it is a bright day, you will see a lot of squinty eyes and other signs of discomfort. Also, this type of lighting has the harshest shadows and can require a reflector or a fill flash to counteract it. Over time, you will find this type of lighting provides the least depth and produces less interesting results than side-lighting or back-lighting.
We recommend starting with side-lighting; you will get the best depth in your photographs and will learn more about how light falls. Side-lighting is best suited for black and white photography, where shadows and textures are most important.
Back-lighting is another lighting option. By placing the light source behind your subject, you eliminate any squinting visible with front-lighting. You can easily product a silhoutte effect with plants, people, or translucent items. If you are photographing people, make sure you use a fill flash or a reflector to show details on their faces. A gold reflector is using in producing golden tones, resulting in warm skin tones. It will also soften shadows.
After mastering where you want the lighting source, the other factors become more easy to work with. The time of day will have the next largest impact on your photographs. The quantity and color of light change most rapidly early in the morning (sunrise) and late in the evening (sunset). Contrary to what you might think, although there is the most light at noon, this is not the best time to take your photographs - the lighting will be harsh and the lack of shadows will make the photography appear flat. Instead, we recommend scheduling photo shoots outdoors for mid-morning and/or mid-afternoon, when you will have plenty of light, but also enough shadows to show depth and make your photograph eye catching.
The weather can also impact the quanity and color of light; if it is extremely overcast, you may not have enough light to work with. Also, a lot of people will not want to chance getting wet, so you may end up needing to reschedule. Mist can have the interesting effect of subdueing the light, making diffent colors stand out while decreasing the details. A lightly overcast day is perhaps the best day to shoot, as your astmosphere will act like a giant light diffusing softbox. Also, it will help eliminate squinty eyes on your subject caused on bright, sunny days. On overly cloudy days, make sure you use a tripod.
Also, make sure to consider your sky. Cloudless days are pretty if you are planning a picnic or day at the pool, but they make for boring photography. Use clouds to make your sky an interesting element of the photo.
Lastly, have fun and don't be afraid to experiment. There are many unknowns in outdoor photography, and understanding how to work with them takes experience.