RUN! Don't do it!
OK, if you must do it, be really sure it's what you want. It's like teaching. You do it because you love it and have a passion for it, and for no other reason (especially not for money.)
Secondly, get educated every way you can. Here, books, seminars, classes, read your state statutes. Get the right training and keep your knowledge up to date with monthly training forums.
Lastly, treat your customers the way you want to be treated- not the way they treat you. Consider it a compliment when they bear their worst side to you (which is normally only seen by family.) Because you hold their fate in your hands your customers will sometimes act out negatively towards you in desperation. Try to put yourself in their place and respond with compassion.