What am i doing wrong with disciplining my 4 year old?

I have a wonderfully bright 4 year old, smart beyond her years. Lately I have noticed I am yelling more that getting my point across when it comes to discipline. Her father and I have been separated since she was 1. With our week to week visitation she has 2 houses with 2 sets of rules. Her father has a different approach when it comes to discipline. I don't believe in hitting a child to get them to listen(as he does) so I find myself constantly yelling to get her to do what she needs to or even to get her to eat dinner. I don't want to be that mom and I have less patience lately with her. Is there an easier way to get her to do everyday things or to even listen to me w/o having to yell at her? Even getting her to eat her dinner is a chore that ends in a yelling match and it makes me feel horrible inside to see her crying when I am trying to get her to listen. Any adivce from separated parents in similar situations? I have a current live in b/f who is exceptionally great w/her