Nature's Mystical Mirrors

The first thing in preparing to photograph water reflections is be prepared to get in it. Tripods that can handle being in the water, waders, and a zoom lens for when you can't get that close because of obstacles.
The best time for reflections is before and after sunrise. Since that means you will be out in the dark, you need to know where to go and how to get out beforehand.
The hardest thing about getting reflections is that you have to wait for the water to be still. The best times are dusk and dawn, but even then sometimes you just have to wait. Wind is less likely in areas with buffers. To keep from seeing the pool's bottom instead of reflection, place the tripod low.
Using a density filter brings the contrast of the picture out more clearly. To best do this, you will need a polarizing filter, a one stop split density filter, and a filter holder. Attach the polarizing filter, adjust it to dark so the reflection from the water is most distinct. Check the histogram to make sure everything is centered in it for good lighting ratios.
A two stop split density filter can be used to darken overly bright skies and snowy mountains. Shading both the object and its reflection brings the shadows into a range the camera can more easily detect. You will need to adjust the filters to fit along the angle of the border betweeen land and reflection, since it is rarely in an even horizontal line.