I think one of the least thought about aspects of being a lone parent is that when your kids are totally, utterly, pushing you to the limit and beyond, nobody comes in to give you a time out to swallow your impatience, re centre yourself and then go back in and deal calmly with the situation.
Somehow you have to find the strength within yourself to find your calm and happy place, even when your kids seem determined to push you to the edge of the cliff and straight over.
I don't always manage it, and that's when I shout, and throw around stupid ultimatums, and rather than calming a situation I too ramp up the tension so that everyone is at boiling point. Accept that you're human and sometimes you won't manage every situation exactly right. Sometimes I can HEAR the voice in the back of my head saying "calm down, you're losing it" but it's gone too far and it's too late, the shouting happens anyway.
Identify your flash point and work wayyyyy in advance to avoid. So if bedtime is an issue, when you're all exhausted and tempers fray, get them into pjs before dinner. So at that point you're not at the end of your tether and once bedtime comes they are only brushing teeth - it doesn't seem such a challenge. Or if it's getting out of the house in the morning, start the night before with setting everything out so that the breakfast table is ready and bags just have to be grabbed etc etc.
Sometimes I really do find it helps to count to ten. During that counting time it often occurs to me that the problem isnt that they're being fucking idiots about clearing their dishes from the table, the real problem is that they're tired and I'm rushing them when actually I could just hold off, or maybe I want them to turn off the tv and I'm ready to shout and lose my rag, but actually the rest of the cartoon is only ten minutes so maybe I could bargain and say when the cartoon is finished its time to go, or whatever.
Count to ten, leave the room and scream into a pillow (helps to relieve tension so you then re-enter the room calmly and able to address the problem), but most of all don't be harsh on yourself. Your kids are human with human emotions and sometimes they're tired and grotty and it's to be expected, but equally sometimes you yourself are tired and grotty and you're only human too. Don't beat yourself up.