You should register and then post some pictures with their exif data so we can help. You should also look at our article section for tips on exposure, as there's a lot of stuff involved in flash photography.
It would also help to know what brand/model flash you are using, and what camera/flash modes you are using (manual, auto, ttl, etc.).
For example, if you are using a Pentax p-ttl compatible flash, it should give pretty good exposures with no real problems. If, however, it is an older flash, or one that is not p-ttl capable, then the issues are more complicated.
As Adam suggested, register and post some photos, with exif data intact. Also post more detail about your equipment and what settings you are using.