S.,
I'm glad you asked your question because I benefited from reading all the answers. I don't hold grudges, but do I think I get mad too quickly and yell too often. Here's what I have done to try to change my bad reactions.
1. I pray with my children every night and one of the things I pray for is that their father and I will be patient with them. If I know it's going to be a bad day (due to lack of sleep or whatever), I also pray in the morning for an extra dose of patience.
2. I try to remind myself of how few years my 3 year old has under her belt. They act so old at this age -- using big words, helping us around the house, dressing themselves-- that sometimes I forget as far as social behaivor is concerned, our little ones have very little experience, and it's our job to help them learn as they go. I try to remember God has given me these children as a gift, and He expects me to teach them to become the people He wants us to be.
3. I try to remember that God (and my husband too!) forgives me for doing things just as bad or worse than what my daughter does, and I'm not 3 anymore. I should know better.
4. I use humor. Instead of yelling "What are you thinking?!", I yell, "Good googa mooga!" It helps me let off a little of that steam that's building up by shouting, and it cracks my daughter up. She thinks it's hilarious, so she starts laughing, and there's nothing like the sound of my children laughing to help restore my good mood.
5. I also try to be silly when appropriate. If it's a minor offensive that was probably done absent-mindedly, then I tell my daughter if she doesn't stop (kicking the table, whining, etc.) that I am going to tickle her silly. She has to say, "I love you Momma" to make me stop tickling. So, her minor misbehaviors usually end with laughter and hugs instead of yelling.
Don't forget to pray. Best wishes,
A.