If you find that some of your mixes for advertising and television sound sterile or harsh, then maybe you can use this little trick to help.
Look at the EQ graph of your dialog (on the right) and find your peaks. (red squares) Then match the EQ slope in your backgrounds (on the left) by digging holes in the line. then you can raise the overall level by 5 to 8db. You'll find that the mix becomes fuller and more dynamic without covering the dialog track.