Try the different exposure modes your camera has to offer. An auto exposure will average the light level from the entire photo and suggest the best exposure settings but in high contrast shots (ie bright sky with dark foreground) this setting can fool the meter. Try partial or spot meter settings in this case. Use the auto focus points in the viewfinder by first pointing at the area you wish to best expose for. Press the shutter button half way and set your exposure based on that measurement. Then recompose the shot and take the photo without changing your exposure settings.