A book I read when my children were little that helped tremendously was 1-2-3 Magic by Thomas Phelan. Yes, it uses counting but that wasn't the main focus for me. The important part was how you use it. First, you create really clear rules with a really clear consequence. Then, when you use the counting you simply count 1, then restate the rule and consequence, then shut up. It was the shutting up that helped me to start removing myself from the emotional battle that would usually ensue. On 3, they simply receive the consequence, no argueing, no convincing, no pleading. Of course, sometimes I struggled with creating an appropriate consequence, but with some practice and creativity, it got easier.
I also learned not to hesitate in removing my children from a situation such as a meeting or being in the store. The great thing about children is how fast they learn. I had to leave an entire cart full at the store one day because my youngest just lost it and I picked him up and just left the store. (He was screaming the whole way out of the store, I just stayed really quit, stuck him in his car seat, and drove home. Even the other two were completely silent.) He got the message loud and clear and I never had a severe incident with him again. Yes, it may be terribly inconvenient such as leaving a school meeting, but it will only take one or maybe two times generally (if you can be very consistent).
Another thing I learned was to be more prepared when I went anywhere with the kids. They each had tiny backpacks that we packed their favorite type of toys, paper, crayons, etc. These stayed packed and they only played with those toys when we went somewhere. I also made sure I had little snacks, such as animal crackers, and water everywhere I went. Again, at first it seemed hard to always remember everything in the rush of getting three kids and myself out the door, but it really made a huge difference and it became motivating to be prepared when I walked out the door.
Hope some of my experience will be helpful. :)