The best light is always early in the morning or late afternoon when the sun is setting.
In low light, a tripod will help you get a good shot at a low ISO. A polarizing filter helps to control glare on reflective surfaces or at least reduce its strength. A gradient filter will also stop the sky being over-exposed. If you do not have a filter, shoot at two different exposures and then combine them in post-production.
Purists may object, but it is the same technique as once used in the darkroom. As for the composition, nothing is better than using symmetry. Let the reflected portion occupy at least half of the photo, or even most of it.
For backlighting, the first thing to consider is if you want to leave the people or any other objects in the picture perfectly silhouetted in black against the sun with no detail. If so, you only need to take your exposure setting from the brightest part (don't look into the sun, obviously), or even underexpose a stop, to maximize contrast. If you want to save the shadows, use a fill-in flash.
As for the composition, nothing is better than using symmetry.
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