(1) Wearing ill-fitted clothes on your interview: Let's face it. Very few of us can still fit into our pre-baby clothes. It is not so much that we have gained weight as it is that our bodies tend to shift and change with each pregnancy. Whereas your girls used to fill a B cup with extra padding, you might find that after the baby comes along your C cup runneth over. There is no excuse for professional women to try to cram their size ten bodies into size six suits. It will impress no one, and you may just overhear the receptionist discussing your "muffin-top" (you know, where your fat bubbles over your waistband, not unlike a muffin bubbling over the top of a tin) while you head out the door.
(2) Wearing too much perfume: When I was in graduate school, I had a professor who asked us to never wear cologne or perfume to class. She claimed that she was allergic to it. After I graduated, we forged a friendship, and she admitted to me that she was not, in fact, allergic. She just found some scents to be so offensive that she could not concentrate on giving her lecture. In fact, she once turned a very promising student down for an internship due to this undergad's foul-smelling perfume.
(3) Answering the cell phone, just in case: I am assuming that you have left Junior in the capable hands of someone you trust. So relax, turn off the cell phone, and concentrate on wowing your prospective new boss. Nothing turns potential employers off more that realizing that there is someone or something more important to the person that they are interviewing. And seriously, what is so important that it cannot wait until you are done interviewing?