Front, Back or Side
I can remember old Kodak educational materials advising that you should always have the sun in the eyes of your subject so they are well lit. But that really isn't very good advice for most situations.
Whatever it is you may be interested in photographing, the light that naturally shines on it varies throughout the day. Most importantly for the topic at hand, the angle of incident light changes as the sun makes its arc across the sky from sunrise to sunset. If you're shooting towards the east, you will be looking into the sun in the morning while the sun will be to your back in the afternoon. At the same time, the light on that subject in front of you will change angles in reverse. In the morning, the light would be shining on the back of your subject. Throughout the day, the light would transition along its side, and in the evening it would be from the front.
That progression can drastically change what your subject looks like. If you want it to look its most flattering, you'll need to be there to photograph it at the right time. I've written before about how odd it seems to me that families judge what Mount Rainier here in Washington state looks like based on visiting it when the time is convenient to them, not when the light is flattering to the mountain. The Paradise visitors center is on the south side of the mountain, meaning you are looking generally north to view its summit. As the sun moves through the sky, it doesn't travel directly overhead. This far north, it's arc noticeably hugs closer to the southern sky than the north, meaning that it is shining directly on the face of the mountain when looking north at lunch.
But that front lighting Kodak used to recommend in beginning photography brochures from my youth can create very unflattering, harsh light on many subjects, including that large white, snow-covered mountain peak here in the Washington Cascades known as Mount Rainier.
Side lighting on Mt. Rainier near Paradise at first light
There are some advantages of front lighting of course. That's why Kodak recommended it. You can clearly see your subject without undo shadows. Lacking significant shadows, it will be easier to retain details throughout the shot without burning out the highlights or losing portions to deep shadows. Exposure times tend to be shorter in such bright, even light making it easier to hand hold a camera without blurring.
But for exactly the same reasons, front lighting tends to produce all-too-even illumination resulting in flat, uninteresting images. People photographed in severe front lighting will yield images that look more like police mug shots than memorable images you will be proud of. Even if your subject isn't squinting, they may as well be. Lacking any contrast, the appearance of dimensionality will be diminished and the potential for drama will be lost.
Back lighting is just the opposite, trading full brightness for full shadows. With the sun behind the subject, it will be shining into the eyes of the photographer as well as the lens of the camera. Now your subject won't be squinting, but you may be, and your camera lens may suffer from notable lens flare. And the difference in brightness between your shadowed subject and the bright sun and sky behind it will likely yield too much contrast to retain detail in both. At the same time, the low lighting levels on the subject itself will mean poor contrast where you want it most.
A backlit subject isn't always a loss though since such lighting can certainly make that subject pop out from the background. Indeed, this is the lighting conditions that can yield "rim lighting" on subjects with fur or rough edges that will pick up that back lighting and scatter it. Scrupulous lens cleaning can minimize flare and newer HDR (high dynamic range) compositing techniques can let you overcome the harsh foreground/background contrast problems letting you actually render the sun and your subject acceptably to create very dramatic images that defy ordinary rules for image capture.
Side lighting is generally the easiest to deal with while still creating great images. When looking up and Mount Rainier from Paradise, the sun is to the side at sunrise creating both beautiful colors and excellent but manageable contrast that highlights the dimensionality of the mountain crags. Side lighting allows you to see the separation between sky and land as well as the details and texture of the landscape in front of you.
Not everything looks good under side lighting of course, but most do. Sometimes there's still too much contrast to get good images. Some subject such as intimate portraits of people and wildflowers benefit from even, diffuse lighting with no strong sense of lighting direction. But I'll save this topic for next week.