On board flash is simply a very poor second choice. If you're going to enter into flash photography you need to know it's strengths and weaknesses
http://strobist.blogspot.com/
If you just want to stick with the inbuilt flash on your Nikon and you're shooting indoors, get yourself some white card, place it under the flash and bounce the light of the ceiling (if it's low enough). The light will be less harsh and it will save on blinks. It's not the be all and end all, but it's better then simply hitting them head on. Just practice, it's not difficult.
But as i said, if you're going to enter in to flash photography, take it off camera when you can
What uses having a great depth of field, if there is not an adequate depth of feeling? -
W. Eugene Smith