Jason,
Same as in any other aspect of photography.
Lighting and composition.
Best time is either sunrise or sunset, and maybe 45 minutes after and before these times.
24 or 35mm lenses are best, although don't discount a short telephoto, like 105-135mm.
As far as composition, a good general rule is to have something in the foreground, middle ground and background - this may mean some bushes/grass in the foreground, a bunker in the middle and the green beyond, for example.
Further, don't place the horizon along the centre - a little off centre is okay, but, depending on the colours in the sky, you may want to emphasise either the sky or ground.
If you divide your camera screen into thirds across, and thirds horizontally, those four intersecting points are excellent places to put some object of interest, because the eye naturally falls to those points, but it isn't a cast iron rule.
Finally, if you are shooting colour, you will generally want a grey graduate filter to darken down the sky a little, and maybe a 81 series warm-up filter to make the most of any soft yellow evening light.
A polariser is also quite good, but I wouldn't use more than two of the three at any one time.