The first time you trying distilling something, it is quite likely that your spirit will taste downright bad. You may describe the taste as "wet cardboard" or a wide variety of other things. In any case, flavoring and aging will help.
One of the first things to try in order to improve a spirit is letting the spirit air out a bit. This is as simple as replacing the cork in the bottle with a piece of cheesecloth. You will lose some alcohol to evaporation, but the spirit will most likely taste a lot better.
Next, in order to further take the edge off of foul tasting alcohol, try adding a bit of sherry to it. This will act as a smoothing agent.
Finally if all else fails, try redistilling the spirit if you can't improve the taste.