I use my speedlights at 1/4 power most of the time in manual mode.Speedlights, or external flashes, are great tools and in my view absolutely necessary for every photographer to own. They are actually very easy to use for the most part. Current speedlights have TTL (through the lens) modes which are basically automatic modes. You connect the speedlight to your DSLR's hotshoe, and the camera's meter determine's the power used by the speedlight. This sounds great, and is convenient, but the problem is often too much power is used resulting in black images. Why? Because speedlights need time to recycle their charges between flashes. The more power used, the longer the time.
This is why a majority of the time I use my speedlights at 1/4 power and always in manual mode. At this quarter power setting the speedlight can take a small burst of shots (3+ in a row) allowing me to capture action in events, group shots, etc without having one of those frames be pure black because the flash did not fire due to a long recycle time.
Try using your speedlight in manual mode at 1/4 power and then compensate for any exposure needs using the settings on your DSLR. You will get more consistent results and your speedlight's batteries will last longer too!