I use a strong, firm voice, not shouting or particularly quiet, just very firm/cross sounding if I'm getting cross.
Don't know how old your DC is but I used 1-2-3 when she was younger, this was what worked the best i think. "I'm going to count to 3 and if you don't do X, then Y will happen" or "if you don't stop doing X then Y will happen". Y had to be something related, i don't really go in for punishment for the sake of punishment. Then count 1-2-3 and carry out the threat. After a while I didn't even have to give a consequence i just started counting & it worked! Until she got old enough to say "Then what?"
When she was even smaller than that (under 2) I gave in to a sticker chart and i admit it worked wonders for our relationship.
I think another key thing is to give enough time. Kids are often so engrossed in their playing etc that they won't instantly do what you want them to do. So I used to give her a concrete time scale or deadline first (5 mins, dd; 2 mins dd; 1 min dd - or even better, something they would understand better, eg when you've put all those toys in the box, or finished that picture or whatever), and then 1,2,3 comes into effect.
Yes dd did on the whole listen to me. But I think that is because my word was gospel, every time, i didn't start deviating from my threats or promises until she was old enough to understand compromise or to reason with me in a reasonable way, iyswim. (perhaps 4/5 yo?)
Been there! Don't beat yourself up about it, none of us are Supermum! I remember screaming and stamping my feet once, and dd staring at me petrified I also remember turning the radio up full blast when she was having a tantrum so that i could drown her out and prevent myself from losing my cool! Or shut myself in my room (sort of the opposite of Time Out!). god that's awful thinking about it but it was impossible to know what else to do with a full on tantrum that nothing could solve! If i was able to completely ignore the tantrum after a few minutes she would get the message and calm down and then we could have a more rational exchange, and cuddles etc.